It's amazing how much crap builds up in the background, temp files etc.
Without wanting to start a PC vs Mac war, I've had no problems at all since buying an iMac back in September.
But in saying that, I was previously using a Toshiba Satellite, with an AMD processor, and the truly awful windows Vista.
A world of pain with that crap combination!!
Sorry to see support for Windows XP ceasing in April though, as it runs rings around Vista, and my Samsung notebook will just be another expensive paperweight to add to the collection.
