I played with my friend's iPad 2 today.  Thoughts:
What I liked: Waaaaay thinner.  Feels much, much lighter as well.  The roll-up screen cover is pretty dang cool.  Noticeably faster - more "instant".  Yay cameras, finally!
What I didn't like: My iPad 1 is already "fast enough" - apps open in seconds, vs. "a" second.  Cameras are junk - the front-facing camera looks like a low-res Youtube video, and while the back is HD, it was fairly grainy.  The camera on the new iPod Touch beats it by leaps and bounds.  I don't know what they were thinking sticking a VGA camera on an XGA screen for video chat, it looks like garbage.  Cool that you can video chat on it though - definitely better than doing it on an iTouch or iPhone.
Also, and I didn't think it would bother me, but the screen is the same.  I like the screen on my iPad 1 just fine, but keeping the same screen on the iPad 2 just felt 
wrong somehow.  It's thinner, faster, lighter, but looks the same screen-wise.  I dunno.  I have no complaints with the original screen, but it did bother me a bit that the second model didn't have a screen upgrade of some kind, considering it's like 95% of the device 
Still on the fence about upgrading.  I don't really have any reason to, other than just 
wanting the new tech, but it doesn't feel like a very compelling upgrade for me right now.  I will probably upgrade at some point since our first baby is on the way, so it'd be nice to Facetime with family and not have to be near a computer.  If I needed to save weight, I'd snag the new one today, but I carry around a 15-pound laptop, so meh...