An iPhone devotee on one week with an Android Phone (One X) as my daily driver
Disclaimer: I have owned multiple Android devices (Nexus One, Nexus S, Galaxy Nexus, Galaxy Note) in the past, but have always used them alongside my iPhone, mostly for play and development purposes.
This last week I spent with the Rogers version of the HTC One X as my daily driver, leaving the iPhone in the drawer, and this is what I've learned.
1. 3.5" might be the ideal screen size. In any case, 4.7" - at least with the current UI paradigm - is too big, especially with the One X's capacitive buttons. I've always wanted a large screen phone, and loved the size of the Note when I had it. But faced with the need to change apps, type quickly, and hit different areas of the screen, I found one handed operation very challenging. With larger hands, this may be less of a problem, but the One X was rather uncomfortable for me to use on a daily basis, especially when juggling a dog leash, a coffee, or trying to wolf down a hot dog. Yes, I know, I could try not to multitask as much, but that's just my usage pattern, and a 4.7" phone isn't going to work, for me anyway. I could always enjoy the Note, because I was using it as a secondary device, for reading, gaming, etc. when I was focused, had two hands free, or when my interactions were simple (such as flipping a page). I'll give you that the 720p 4.7" display on the One X is indeed beautiful, especially for pictures.
2. The Android UI is beautiful, and, unfortunately, a mess. I love Android's customizability, and the opportunity to put different launchers, widgets, lock screen apps, etc. Stock ICS might be more aesthetically pleasing than iOS. But Sense and Touchwiz are terrible abominations, with unfortunate colour and font choices. The One X hasn't been around long enough to have Custom ROMs available (I'm sure CM9 - when it arrives for the NA version - will be great), so I was stuck using a variety of tweaks (WidgetLocker, GoLauncher, ExDialer etc.) in order to get a stock look. Even then, things weren't quite right and consistent. I'd go to answer a phone call, and couldn't get rid of the HTC phone app. Once in a while, I would see the stock lock screen even though I had replaced it with a custom version meant to mimic Stock ICS.
3. App-wise, Android is almost there. This had been a reason why I didn't try this experiment earlier, but these two ecosystems have almost reached equality. Some Android replacements for iOS apps weren't quite as functional, and clearly iOS devices were still getting the majority of updates first, but they're almost on par now. There are still apps that stood out like a sore thumb or are missing in Android, though. Twitter is pretty terrible, and the third party apps that people recommend are more functional, but ugly as sin (TweetDroid, Twittlelator Pro, etc.); comig from TweetBot, I really missed the refined Twitter experience. I can't believe that there's no official Starbuck app (use it to pay whenever I'm there) or NIke+ app. And several important apps, for me anyway, are generations behind.
4. Apple has me over a barrel. Although the app ecosystem is no longer a concern, I am still too connected to the Apple ecosystem to move over on a permanent basis. Sure, there are ways to sync or merge Apple ecosystem information with Google's system, but there are issues with moving between them. iCal and Google Calendar work fairly well when using a third party app on your computer to do the merging, and Address Book is supposed to work well, but is prone to somewhat odd behaviour sometimes resulting in missing contacts. Apple's iTunes Match is an essential service to me, and I don't want to waste 100GBs of upload bandwidth making my stuff work with Google Play. And Apple, by making iMessage one of the glitchiest apps ever, has basically screwed up SMS for me on non-Apple device. Messages sometimes go via iMessage, sometimes via SMS, and I would miss loads of messages on my One X, only to find them in my SIMless iPhone later on. I also can't go without Visual Voicemail for too long; in order to do that on the One X, I needed to switch plans and features, which I wasn't ready to do for my experiment.
5. LTE is amazing. If the new iPhone doesn't have this, I'm gone. Such a switch will involve a much greater commitment to Google's ecosystem - moving to gMail, Google Play, etc. - but that's one thing that will help me make that jump.
In any case, these are just some thoughts on making the switch. I think both Mobile OSes are fantastic, but at this point, I'm sticking with iOS.