I'm in the same boat, and probably leaving too. I kind of want to see how the battery life on the EVO pans out, and if the iPhone's battery has been improved even further, but baring any huge differences, I'm going Android.
My problem with the iPhone OS is that it has followed a development cycle very similar to OS X. OS X has had a large number of small OS revisions (about every 18 months) that each built a slightly better OS. And most of the changes were mostly back-end functionality. That's fine for a computers OS, since the standard development cycle of Windows is closer to 4 years. You don't want a revolution in your computers OS every year. And besides, the technology isn't changing fast enough to warrant that.
MobileOSes are still in their infancy, and the number of vast hardware improvements, added functionality, new uses, etc are coming at an amazing rate. Apple just hasn't kept up on all of this, and is relying on what is essentially the same platform from 2007. A little faster, a little more storage, a few more bells and whistles. Now, the iPhone UI was easily two-years ahead of its time (which has to be at least 5-7 years in computer OS time), and it has taken this long for someone to catch up.
But they have caught up, and are surpassing the iPhone UI in terms of speed, functionality, and at least rivaling in usability. Apple had the chance to really spice up its offerings with 4.0, but is instead only catching up on features. They aren't innovating, they are refining. The OS is refined enough - it needs a leap ahead!
Now, I am a techie, so these things matter far more to me than the normal user, so I don't expect the masses to abandon apple anytime soon. For as many people are switching to Android for new features, far more will be switching to the iPhone from non-smart phones. Apple has plenty of time to stay in the marketplace and make money. There is a group of users who likes everything the way it is - and they can stay with the iPhone.
Android isn't unstoppable either. If you've seen the Windows 7 Mobile UI, it may have the ability to leapfrog everyone by another year or more. All of the demos I have seen show an UI that is innovate, clean, and (most importantly) data rich. A quick glance at the homescreen tells you most of what you'd want to know on your phone. I don't think I'm going to wait until the end of the year for a mystery phone that I have no other information on just yet, but I'll keep my eye on it, and may jump to it if someone can put up a device that beats the apple and android offerings. Hopefully we will soon see a real competition in the Mobile arena between companies that's going to force some real innovation on all ends. With three in the market, it will be very interesting.
Also, for everyone calling for Steve Job's removal - that is just dumb. The man has made Apple the company it is today. He is an expert salesman, and he knows what the general public wants. These are the same people who claimed that nobody wanted an oversized iPod, only to see the iPad sell 200,000 units a week.