For a long time I was using Ctrl-F4 to close tabs in Netscape which was killer on my fingers (I have a bad habit of using the same hand for the key & modifier). Then, while trying to find someway to save files without bringing up the stupid save dialog box, I found the ctrl-w for closing windows/tabs which works great.
Except that W is next to Q, and ctrl-Q shuts down everything.
Now I was already in the habit of trying to keep bookmarks for open pages and other steps for recovering from a crash, but now I have to worry about shutting everything down on accident when I'm not careful with my fingers.
Its very annoying.