1. Ctrl-W (close window) right next to Ctrl-Q (exit and close all windows in Netscape/Mozilla)
Ever wanted to close one window and accidentally shut down your entire set of browser windows?
2. Ctrl-C (copy) next to Ctrl-V (paste)
Highlight something to copy over it, then accidentally hit Ctrl-C and Ctrl-V together instead of just Ctrl-V...  you copy what's highlighted instead of pasting what you wanted to replace it with. 
What others are there?  
