Since I tweeted about it this morning, loads of people are asking me why I forfeited £29 and went back to Snow Leopard. Well...
Lots of my software stopped working. Apple removed support for Rosetta, meaning a lot of my older software no longer worked. I upgraded Office through a scheme we've got at work for purchasing new Microsoft products, but I just can't afford Adobe CS 5 right now.
Most of Lion's 'upgrades' were just annoying. Mission Control and Launchpad are pointless. The swipe gestures are bizarre (a couple were good, most of them I couldn't remember). And it kept asking me for an administrator password when I wanted to do simple stuff.
Snow Leopard is actually great. It already has the Mac App Store, and is stable and fast. Integration with iPhone and iPad is seamless. And it looks great too. In fact, most of Lion's design tweaks made it look amateur.
It was pretty easy to do - I just reinstalled from the original software that came with my MacBook Air, following these instructions. I'm very glad to be back.