I'm using my 11" Air for work sometimes when traveling. Just last week I was updating a Flash project. I was running Flash CS5 to change some flash content, Photoshop CS5 to edit some images (although quite small, no raw files), Coda for updating some HTML files, Thunderbird, FTP client, as well as a Firefox browser with a few tabs, IM / twitter client and a few other smaller apps (all at once ofc, just tabbing between them).
The only time I ever noticed the Air slowing down was when publishing the Flash content (which is 100% cpu dependant). But, to the Air's defense, it was a 180Mb Flash file that even my i7 iMac takes 20+ seconds to publish. I didn't time it on the Air, but I'm guessing maybe double that time.
Anyway, my point is, everything worked flawlessly. I never noticed lag, extensive swapping, jerky scrolling or something like that. Unless you're editing huge raw images with complex filters you'll be fine.
My Air is the 11.6" 1.6Ghz with 4Gb memory. I strongly recommend 4Gb if you're going to use the computer for photoshop and similar.