I've got a bad habit of accidently hitting the "Insert" key and changing into overtype mode. I sometimes end up replacing several words, sometimes an entire sentence, before I realize what happened. I've never found any use for this "replace" mode, and I can't imaging a scenario where I'd ever want to edit text that way.

If I can't find a solution, I'm gonna break open the keyboard and permanantly disable the "Insert" key.