What EXACTLY is it that you're going to be doing? Games development encompasses a wide range of skills and jobs - are you an artist, programmer, level designer, sound guy, one-man-studio? We need more information to properly assess what your requirements are.
At this point with so little information, all I can do is give you my own experiences as a guide:
I still use my 13" 2010 top spec Air as one of my main machines for it's portability but you need to be clear on whether portability is something you actually need. For me, I move around a lot and need to be able to take my work with me but if that's not a concern then maybe the Air isn't for you.
As for real world scenarios:
- It handles upward of a million polygons absolutely fine in Zbrush,
- Typically have 20-30 Photoshop documents open (texturing, concepting, sprites etc)
- Unity runs absolutely fine, typically takes 10 secs or so to compile a build,
- I use Logic for composition and sound effects and it is also fine.
- 3DS MAX is fine, though really high polycounts can slow it down (we're talking 200k+, for reference - a typical xbox 360 character probably clocks in at under 10k at the highest LOD.)
- On top of all of those running simultaneously, I am also procrastinating online with 20-odd tabs running so I can safely say, the Air is a capable machine.
HOWEVER: I want to reiterate: ONLY GET AN AIR IF PORTABILITY IS THE ABSOLUTE REQUIREMENT, OTHERWISE YOU GET A LOT MORE POWER FOR YOUR BUCK WITH A PRO OR A DESKTOP.
It struggles a bit on things like lightmapping, some kinds of rendering and any intense calculation but these are few and far between - and manageable.
As a whole though, if you REALLY want to get an Air, you should be fine.
Giuseppe
Edit: I'd like to add - YES, you can develop a PS3 game to full quality on an Air. You may run into performance issues running the game at it's intended settings* but you'd probably want to run them on an actual PS3 dev kit if that was the case.
*also with intense calculation during development, light lighting. but in terms of actual content generation (graphics, sound, code itself) the Air is perfectly capable.
All in all though, I highly doubt you're developing next-gen games. If its some kind of mobile game you're doing- the air will be fine.
But frankly, I'd get a huge, beefy iMac or a top end pro and be happy with superb performance guaranteed.