I've been hearing a lot of reports that Age of Conan is a ridiculously demanding game in the vein of crysis, and a lot of people have been upgrading their systems to run it. Keen to see what all the fuss was about I watched my roommate play it on his system and became interested - I decided to install the game on my PC and make my own character for it - so far so good, I'll say more about the game itself once I've played it (and bought it myself...)
For the performance though, I think people are overstating it, really. Remember it's a MMORPG not a cut-throat FPS, so the frame rate tolerances are slightly better. I'd put the 'pleasant' frame cap at 25 rather than the 40 for FPS games. Here's how it runs on his PC and mine:

His PC: X2 4200+, 3GB PC3200, X1900XT-X: 1920x1200 Texture settings maximum, lighting and shadow effects mostly disabled, no AA, no AF - 16 to 25fps.

My PC: E4300@3.15Ghz, 3.5GB PC2 6400 (4GB, OS limited), HD3870: 2560x1600 All settings maximum except shadows and bloom disabled, no AA, 16x AF - 24 to 40fps.

As you can see, a last gen gaming rig will run the game adequately at a high resolution - for full eye candy you're looking at standard resolutions like 1280x1024, but very doable. Even with a singular current gen card, performance at a very high resolution is admirable. For full lighting settings at 2560x1600 you'll want a bit more, but unless you absolutely max the game on a 24"+ screen, you'll do fine.

As far as I'm concerned, Crysis remains the most demanding game for the PC for playability - frame rate wise, Age of Conan manages about the same, but given the fact that it will be playable at a lower FPS, I brand it 'less demanding than Crysis'.