I agree that it *can* get bloated and start crashing. My mother's PC does that. She loads it down with webshots and any number of other things, allows a toolbar in there, doesn't weed out launch-ready programs that keep running for apple products, for MS office, etc.
However I think (strongly) that if you keep your PC fairly trim, you turn off all those preloaded annoyances, that you can run a CAD program and it won't impact your system until it is up and running. If you run a game it won't impact your system until you execute it. You can pick and choose any particular program to suit your needs and not load it a second before then, I mean. Until then it's just taking up clusters on the HDD.