Windows ex-pee
I got a good laugh today from this article from Newsbytes reporting the cause of random words that are inserted into documents when using Windows XP or Office XP.
It turns out that some computers ship Windows XP/Office XP with the built-in speech recognition software enabled (unbeknownst to the user) and if you have a microphone attached, it tries to take dictation. So the side effect is that you're humming your favorite tune as you write an email and as you're typing, the computer is trying to decipher what you're 'saying' and interjects 'baw em bop be duh do' or something to that effect.
Here's the Microsoft support document about the problem.