My 12" iBook g4 1.33ghz with 768mb of ram and a 4200rpm hdd has been my main computer for quite some time. I've made movies on it, pictures, internet, email, microsoft office, all with ease. Granted it's not as fast as I would like.
But for someone like me, a macbook air is ALREADY going to be much faster than what I have. Most of the people crying are ones with MBP's or Macbook's saying oh man this thing is slow blah blah. Well ya, duh! It's slower than your computer, so what. Don't buy it, but it works for some people, and it's benefits to me outweigh what it's lacking.