- Totem said they where *playing*, but the progress bar wasn't moving and there was neither sound nor video.
- The time counter (shows how many seconds/minutes into the video/song you're in) wasn't moving.
- I thought it was something wrong with the newly mangled videos (made smaller via ffmpeg) so I tried some MP3s. Same symptoms as for the videos.
So I looked around at the modules, and at dmesg. Everything looked good. Until I moved my mouse to the bottom of the screen and the hidden status panel popped up. Skype was running. Apparently, on this machine, it takes over the sound card.