Here's my point: It looks like the 3GS is the better camera for macro photos and for shots in excellent light. But if you want a camera that captures more information in less bits, the old 2G (or 3G) camera was clearly a better camera. I hope the third generation of iPhone cameras leapfrogs the 3GS one and gives the best of both worlds. A lot of people on this thread are gushing about the new 3GS camera. My point is: the 2G camera was better in many ways. (But I must confess: the macro shots are great. I tested those too, but there's no need to put them up here as there are tons of these up here already.) I just wanted to prove that for people and faces, the old 2G was a better camera. Think: you can still get one now for only $99.
Thanks for taking the time to do those side by side pics. As someone else mentioned, the biggest difference between the 2 seems to be exposure.
In the first set, the 3G seems to have a better exposure reading, the 3GS is underexposed a bit.
In the second set, I think the 3GS actually does better. The 3G shot definitely has blown-out highlights. It's actually a very contrasty scene which makes it challenging for even a regular compact digicam.
In general, it's better to underexpose a bit than to overexpose, because you can often recover detail in darker areas. OTOH, most people are going to be doing any Photoshop with iPhone pics so maybe the metering in the 3G is better (at least in the comparison shots you posted.)