It's not the software itself that'll give you problems, I run mine on a 11" with just 2GB, for simple editing stuff with smaller happy snap sized files (say up to 10mb files) it works fine. It also loads up nice and quick and is surprisingly usable.
However, if you start trying to open multiple files, multiple layers and RAW files, then you will notice the limits of the Air, after all thats not really what it was designed for.
So, yes for your everyday casual CS5 user, go for it, you won't be disappointed if you don't demand too much of it.
This is what I was going to say, its not a problem of the app not running, its whether or not you can actually be productive with it.