How many songs do you need for an office playlist?

If you were going to plug an ipod into a pair of speakers and make it your office background music machine, how big would the playlist have to be so the song repetitions wouldn’t drive you nuts?

Based on a 4-minute per song estimate, that would mean 120 songs per day, or 600 songs per 40 hour work week without a repetition.

Moved from IMHO to CS. (With some doubt, but it should do well there.)