I just switched from Eris to Motorola...
Well, I actually had the HTC Eris Droid for 5 days... during which I used it relentlessly. I liked a lot of things about it... but ultimately... there were a few issues that (although seemingly minor) became so irritating, so quickly, that I went back to the Verizon store to play around with the Motorola version. To make a long story short... I returned the Eris, PRONTO, and picked this phone up (the Motorola Droid).
There are many reasons, but chiefly... it's a much more solid phone than the Eris. It's heavier... but I actually like that. It doesn't require a case... the Eris does (which makes it about the same size). And while i appreciate the physical keyboard, and use it about 50% of the time... the fact that the Motorola droid's screen is nearly .5" larger than the Eris screen, means that their (horizontal) virtual keyboard is WAY roomier than the Eris keyboard. Just comparing the 2 virtual keyboards, side by side... I can tell you first hand that I'm typing 10x's more accurately with the Motorola VIRTUAL keyboard, than I did with the Eris.
The Eris ran a little slower (because of the slower processor... not just the inferior operating system)... I could never pull down the 'alerts' messages on the first (or second) try... whereas with the Motorola it's a simple swipe. It's just much easier for me to use the Motorola, than it was for me to use the Eris... and I don't have large hands (and I'm an illustrator... so my fingers are rather dexterous!). The HTC seems designed for women with small hands... while the Motorola was designed with a guy in mind.
If you're trying to choose between the two new Droid phones... speaking as a 30-something guy who enjoys pounding away on various apps for hours at a time... I'd suggest going with the Motorola. The calls sound great... the service is solid (either way)... the screen resolution will blow you away, when you compare a movie played on the two... and it's all the same functionality. The same apps. The same "droid" operating system.
I'm genuinely happy that I returned the HTC. Since I'll have the phone another 2 years, I may as well have the one with the faster processor, nicer camera (flash), better screen, and more memory/storage. Right? That's how I see it.