Just upgraded from an HTC Magic (old, but I like it) to the Google/Samsung Nexus S. I love the pure Android. There are things I miss from the Sense UI, but I can live wihtout them.
I would definitely prefer that I can move a phone forward, rather than have it left behind because of an added UI. Of course, now I won't have to - thank you Google.
@ben850 - what about 2G users - can they use all of the features in iOS 4? How much longer will the 3GS be upgradeable? I appreciate that it is currently supported because my wife has the 3GS (which is a really nice phone). It should stay up to date for a while because the OS and the hardware come from one company. The Android world is more varied over hardware and add-on software, except for the Google phones. They retain control - like Apple, keep pure Android on them, and they update them (not sure how long it can continue as the OS may outstrip the hardware, like the iPhone 2G). The original Google Nexus One has been upgraded to Gingerbread.
For the HTC Magic, maybe it's time to root it and put in one of the mods?