I'm experiencing the exact same issues. It started about a year or so ago, my MacBook "Pro" is out of warranty. At first there were subtle occasional display anomalies, which over time have become more and more severe. It seems to coincide with overheating, I'm going to try a cooling pad and cleaning the fans inside to see if it helps. Right now I'm also looking into getting a new logic board off eBay for a reasonable amount of money to squeeze some more life out of it. It's very irritating as I rely on this machine for work, and I've already spent a lot of money on upgrading it. Since I've had it I've had the battery die very quickly, the magsafe charger die even quicker, the DVD writer fail and recently the trackpad has started to show signs of developing problems. Snow Leopard runs smoother than Leopard, but is more prone to freezing under high CPU load. Not that Leopard is stable for me either - if it goes for one day without crashing at least once, it's a miracle. Earlier today Snow Leopard froze on me seconds after startup on three successive occasions. I can't count the amount of times my MacBook "Pro" has crashed whilst looking at a youtube video. Any page containing flash sends my CPU fans into overdrive. Overall, I'm having to tiptoe round this MacBook "Pro" now like a terminally ill patient and I'm crossing my fingers that it won't die before I get a chance to get a new machine.
Like others have said, this has made me think hard about purchasing another Apple laptop. You live and learn! I might have to go for a PC this time (which is sad because I really like OS X) because I've wasted too much money on this and it's a more cost effective option. If it wasn't for the money I've spent on it I would have probably thrown it out the window and smashed it to pieces. £1000+ is too much money for a "Pro" machine that has a shelf life of a year and a half. I have friends who have experienced issues with their PC laptops, but the difference is that they're paying £300-£400 for theirs not £1000+. For that kind of money you expect the machine to be robust and reliable. I wouldn't risk getting another machine now without Apple Care.