I don’t care if things run slow. I can wait 5, 10, 15 more minutes for something to encode.
I want my user interface to be fast.
I want my windows to move around fast, and I want to switch programs quickly. When I click on menus, I don’t want to wait for disk access to do basic menus.
Biggest offender: Windows XP Start menu — why the hell do you hit my disk when I click start->all programs? It would take so little to cache that.