I had an iPhone on eval for a couple of days, and have learned many things.
iPhone VPN is buggy -- it only accepts numeric passwords (many people have gotten around this; mine hung when I tried), tends to forget them (these are well documented online). It's quite limited -- not compatible with RU's IPsec configuration (we could perhaps fix this if we weren't concerned about attackers using the VPN protocols); not compatible with our (preferred) SSL VPN. It's insufficient -- as Glenn Fleishman pointed out for Macworld, the iPhone won't store multiple IPsec or multiple PPTP VPN configurations, and cannot be configured to always reconnect to VPN when moving between networks.
The iPod functionality doesn't support shuffle by album! It's only by song (which I don't like).
Several people have complained that the iPhone doesn't work with their older earphones. I was pleasantly surprised that it works with my older Apple iPod In-Ear Headphones, although unfortunately it doesn't accept the higher quality UltimateEars 'phones Amy and Julia gave me for my birthday. Most earphone cables have a thicker area around the connector for grabbing to extract the 'phones, and Apple recessed the jack without leaving enough room for those 'handles'.
I thought I could just dump the full-quality MPEGs from our TiVo onto the iPhone, saving the considerable H.264 recompression & scaling time, but they don't work. On the other hand, Dr. Who at 480x320 looks and sounds great. As I try them out, though, I find myself cursing whoever decided not to show file suffixes on the iPhone, or in iTunes, or in the error messages that a file can't be transferred because it's the wrong type. Okay, but which one??? I have a .mov, a .mpeg, and a .m4v -- which is the tall one, which is the good one, and which won't go??? I've made some guesses based on graniness and proportions, but they are guesses, and I shouldn't have to rename the files and spend a few hours transferring and deleting and retransferring to discover what Apple refuses to tell me.
It's great that the iPhone can display PDFs, but annoying that it seems they must be received via email or accessed in real-time via a website.
Pinching doesn't work well one-handed. I tend to spend 2h+ per day walking around or sitting with my Treo 650 in hand, reading or watching video. It's easy to use my thumb to drive the iPhone (or hit keys on the Treo), but no pinch. So to zoom I bring my other thumb to bear, which doesn't work terribly well. Also, due to its size and slipperiness, the iPhone is harder to hold. I dropped it within 24h of getting it. I know the screen is bulletproof, but not the back. I can see marks on the bottom black and the top silver. This is minor, but how many times will I drop an iPhone during its 2-3 year lifetime?
It's annoying that movies must be manually selected in iTunes before they will sync over.
I wish I could set a home page; I have a list of links, and have to keep telling the iPhone to go there. I understand the desire to avoid a heavy page load on connect, but we should be able to have a home page (perhaps even a local one, or start with the Bookmarks list). A wiki would be even better for this; perhaps I'll set up a private one after I get a real iPhone, someday.
Despite the claims that iPhones don't have scrollbars, they actually do. As you flick-scroll through a long document, the iPhone shows a small dark grey proportional scrollbar to give you a sense of position within the document -- a welcome aid to navigation, since when reading there's no indication of how far down the page you are.
I think Apple overcommitted to the "real" Internet in your pocket (meaning something very like Safari on Mac/Windows). Comparing reading the same pages between the Treo 650 and the iPhone, the iPhone was actually inferior. The page loading was slower, since each page had to be downloaded; in contrast, Plucker documents are already in flash, although the CPU can take a few seconds to render them. The iPhone renders all the images, even though on many sites they're purely advertising. Here's a case where Apple's delivering on their claims, but it's a bad thing for usability; a setting (ideally per site) to skip images would be a boon.
Plucker reflows paragraphs to fit the narrow screen width; this works well except on rare pages with hard-wrapped lines. Mobile Safari tries too hard to keep the original web page's column width, meaning many pages are either too tiny to read or can only be read sideways (scrolling twice per line is a non-starter). There's no reason to slavishly honor web designers' specifications for width on a new platform with such different characteristics than these sites were coded for -- perhaps if the iPhone finds an iPhone-specific style sheet its width should be taken seriously, but most web sites just assume 1024x768 or better, and the iPhone suffers needlessly when it tries to play that game. In fairness, some sites, like The Onion AV Club look much better on the iPhone, but the news sites I mostly read don't.
I'm disappointed by the iPhone's font rendering. I can tell it's using 'real' fonts, but anti-aliased Gothic 18 on the Treo is crisper and more readable.
Additionally, when reading web pages and email, you almost always want to scroll a full page. Safari tends to scroll half a page, or a page + 2 lines, or a page down and 1/4" to the right. It's erratic enough that I spend time looking for the last line I read, which is a recurring waste of time. I see that the iPod is trying very hard to respect what I did, but I shouldn't have to start at the bottom, drag to the top, and watch how far it went. I should just make the "scroll" gesture and it should Do the Right Thing, since WIM is obvious.
I do like that (unlike the iPod) the iPhone is usable while plugged in, and can always be disconnected quickly (the iPhone Dock connector doesn't lock like the iPod connector); this is partially because it's not accessed as a hard disk, and partially because people like to charge their phones but still need to answer (make) calls. In contrast, iPods are largely superseded by iTunes and speakers on the computer they plug into.
Bug or design flaw? With the mute button engaged, iPod mode still plays sound on videos. If I have mute engaged, the speaker should be off. Not "only on for those things Apple believes I probably really want to hear anyway", but off. I haven't checked YouTube.
Speaking of which, it's ironic that a small screen with a relatively slow CPU and network connection is such an excellent YouTube device, but that will remain true until Google makes the H.264 streams available through their normal website.
I haven't really used the MobileMail. The PIN isn't adequate security, so I've only trusted it with my unused .Mac account.
I haven't used the calendar much -- I'm working under some unusual constraints, and 2 days isn't enough to switch myself to looking at the iPhone for calendaring, but I find the absence of Week view inexplicable.
I haven't used Visual Voicemail! Rockefeller has a (poor) Windows-based voicemail app which I use sometimes, either to avoid switching headsets or for better control than button mashing. Interestingly, Apple's iPhone implementation looks substantially better, despite the physical constraints. I always knew the app stunk, but apparently the modern ones are all purely Exchange based. Perhaps we'll see some improvements in this area.
Here's a silly one: the iPhone gets dirty so easily that wiping it off wastes a few minutes each day. I have better things to do with my time than polish an (admittedly beautiful) Apple iPhone. Watching video is the worst, since the controls are all onscreen and don't work well with fingernails. After picking a video and hitting Play/Pause a couple times, it gets notably harder to see.
Video controls are poor. They're hard to hit, don't always trigger, and accelerate as you hold them down. The result is that by the end of a commercial break, once I see the show and release, the iPhone has jumped substantially past the end. Then I go back, and often have to watch the last commerical again (3x total: once fast forward, once fast backward, once normal forward) to get to the resumption of the program. Dragging the time slider is way too imprecise. These are fixable in software, and hopefully they will be soon.