Search in the start menu. I can’t stand XP’s menus on the start button. I’ve got at least 4 machines, each with different ways of categorizing things in the start menu. They all are way too cluttered to spot anything, and I loathe every time I have to go these menus. With Vista, all you do is search. Type “e”, and you are already at Excel. Type “programs” and you’re in the control panel. It’s just great.
I realize you can buy add-on products to XP to do this. Maybe I will. This is the most visible feature that I miss from Vista.