Well i've been using CS5 all day, just goofing around. Please note that I'm not a professional graphic artist or anything, i'm a hobbiest photographer with about 10 years exeperience using photoshop as a hobiest so my results may be different than your.
So far, I've found no issues running CS5. I've been using the spot healing tool to do some content aware editing (Power Line removal, people in the backgroup, trash cans and street cones) and havn't run into any issues. Its actually been quite fast for my liking.
For comparison issues, 2 months ago I was running on a single core AMD from 2004 with a xfx nvidia 7800gt using 1gb DDR
Now I'm running an i7 860 with 4gb DDR3 on a ATI 5760 HD
I would say the MBA with 1.8g and 2gb ram is running much more like my i7 than my AMD. I would suggest getting the 4GB of ram model, just to furture proof yourself. I'm probably going to wait a week or so and return my 2gb model for a 4gb model. (I acted on impulse when they hit the stores)'
Tonight i'll go ahead and install noise ninja, because that seems to be a very demanding plug-in for CS5 and will give my reports on that as well.
Aside from fraps, is there any recording software I could use to show you guys videos of the processes in action?