The A/V sync problem...
Film and analog video have one admirable feature that digital video lacks: sprocket holes. For over 80 years sprocket holes have done a superb job of keeping picture and sound in sync, providing a mechanical point of reference for each. Of course analog videotape never really had sprocket holes, but it had the electronic equivalent, in the form of sync pulses marking each video frame.
As our featured article in Video/Imaging DesignLine this week explains in more detail, compressed and digitally transmitted digital video has unlocked picture and sound, wreaking havoc on synchronization (see HDMI's Lip Sync and audio-video synchronization for broadcast and home video.)
The problem ultimately requires feedback from the TV or display -- because how else can you know the delays that video signal processing is introducing, including delays caused by scaling and other processes within the television itself?
It's a big problem, and the HDMI Lip Sync spec doesn't provide the complete solution, but it's an important first step that CE manufacturers should broadly adopt (like most new aspects of HDMI 1.3, Lip Sync is voluntary.) It also makes one yearn for the good old days of sprocket holes.