I grabbed a fully loaded 20". Max RAM, best vid card, etc.
Here's some quick takes, with no thorough testing.
Photoshop is perfectly usable. As Steve said, if it's not your full time job doing Photoshop work, you'll be fine until the UB.
Carrara/Hexagon. GUI is not as smooth, I'd guess around 20+fps. But in terms of actually using the apps (modeling, for example), it's perfectly usable. I emailed Eovia on a timeline for the UB and they aren't offering anything publicly in terms of a timeline. Looks like I'm switching to Modo sooner than I thought.
World of Warcraft. If you stay in a dungeon, it's glass. If you go outside, it gets very choppy even at low resolutions. Buy hey, the UB's coming in two weeks and the early reports are that it's FAST:
http://arstechnica.com/journals/apple.ars/2006/1/12/2478
I played it for the first time for a couple hours last night. It's playable, but barely. If I didn't know the UB was coming, I wouldn't play it via Rosetta.
Misc apps are hit or miss. Multiplex (movie player) hiccuped a lot on playback, but VLC runs like glass.
Funny thing is that I bought the thing for home use (iMovie for home movies type stuff) and I have yet to even play with the iLife apps cuz I've been goofing off with non-native apps. Presumably they run quite well.
Actually, I did get going on iPhoto and it runs great. Not super dooper silky fast, but nice and zippy. GUI is solidly fast and all the effects are instant. Like instant instant, no delay whatsoever.
Overall the GUI on the Intel Mac is way fast. Slightly faster than my Dual 2.7 G5, so that's pretty fast. And Spotlight is faster on my iMac than the dual G5, but that may be in part due to having much less content to wade through.
My early review is that it's a compromise machine right now due to Rosetta. If you need to run certain apps at full speed, you may be better off with a G5. If you're like me and willing to endure the months of nativifying (I just made that up), it seems clear that this machine is going to deliver.