I just tested it with iTunes; after switching the user account (only after logging into another account, to be precise) the audio playback from the account "A" stops. However iTunes continues playing in the background; which I realized after switching back to account "A".

Very frustrating because it kind-of is a deal-breaker for me; the other person should be able to have some personalized settings; while it is still my computer, and the main account has all the music obviously. The ideal solution would be audio output continuing running while user still has the ability to manually pause it...

EDIT: I tested a bit more: "Desktop" apps like VLC don't output sound but continue running; the stock Music.app in Metro pauses the music and continues playing when switching back.