A number of reasons, which I will now list in exact priority order.
AT&T sucks ASS. Now this is not due to a lack of trying to improve on their part. I admire and acknowledge the fact that they have recently increased coverage in Noe Valley, Diamond Heights and Glen Park. My iPhone now works in Safeway (sometimes), which is a vast improvement. However, present improvements cannot overcome other misdeeds. For example, the hours and hours of wait time when I rarely have to call customer service, or the dropped calls in my house with full signal, or constantly drop on 101 while dirving? I am completely convinced that AT&T employs subpar network engineers. How is it that I can get 5 bars in my house and consistently drop calls? The Verizon network is far better.
The iPhone is the buggiest phone I've ever had and I believe Google has far better engineers than Apple. If Android has even 25% less bugs, that will be a huge improvement. On the iPhone, apps crash constantly and there are new glitches all the time. iPhone 3.0 introduced possibly the most annoying bug of all time, which is that the iPhone now constantly asks for my wi-fi password at home. Today had a nice glitch where I couldn't get rid of the keyboard from the screen. Just poor programming all around. I have not yet heard of that range of problems with Android.
Google integration > Apple integration. My MobileMess subscription is running out in 4 days and I, of course, do not plan to renew. One of the problems with the iPhone is that I can only have Exchange connected to one server plus MobileMess. I'm hoping that Android will let me connect to one Exchange server as well as Google Apps, which is where all of my real data is anyway.
Real background apps, please. Kthxbye.
I would much prefer a smartphone that I have a prayer of programming. I refuse to buy a Mac just to program my iPhone, and besides, I can't upload my own apps to it anyway. No thanks. I'll take the open option that I can hack the crap out of--legally--if I so choose.
No more iTunes!
So anyway, these are some of the reasons I'll be camping out to get my Motorola Sholes or HTC Android device on Verizon as soon as they arrive.