I am a mac support engineer in the UK. In my experience most issues can be dealt with by booting onto a firewire backup of your system (probably created with Carbon Copy Cloner). Then running The Disk Utility to repair permissions and something like Drive Ten to optimize the volume. If you have trouble booting to another volume try starting holding the alt+option key and selecting the disk from the boot screen. I run around 15 macs, 50/50 desktops/laptops all OSX none experiencing problems.
Apple and The Blue Screen of Death, the Truth