This is weird. I'm not sure when it happened -- I just noticed it when I switched back into iTunes just now. I definitely haven't installed anything between when it was working and when this happened, though.
My iTunes Party Shuffle playlist now displays my entire library, no matter what the playlist source is set to, or what the number of upcoming/recently played songs drop-downs are set to. I've refreshed it several times. It just shows my entire library in alphabetical album-by-artist order. I've quit and re-opened iTunes several times, deleted its preferences, logged out and logged back in again, and restarted. No dice.
Any advice?
Edit, should have mentioned: iTunes 7.4.2 and OS 10.4.10.