One of the main problems with moving from the iPhone to an Android-powered device is the fact that at least twice a week you're hearing about a new Android device on the horizon that makes yours look like an ancient artifact. Basically, if you have an Android phone that you didn't buy within the month, your phone is old news.

Here's a good example:

This device is the HTC Dragon, from Samsung, and it's supposed to be awesome. Looks good, right? Nope. There's a true Google phone coming after it that's supposed to be much better.

Bottom line: with the iPhone you rarely have to deal with hardware envy for a solid year, whereas if you go with Android it's going to be a constant issue.