I'm having this issue as well.
Interesting sidenote (I thought anyway). I have a HDMI vid card and run the connection through a Onkyo 805 receiver. This is just for testing as a MD will eventually be connected through the Onkyo with SPDIF surround sound. Currently I'm running a stereo to RCA adapter to the receiver. I noticed the video is a little faster than the sounds (mouth opens, count to 10-20ms and the sounds hits). This confused me because I was always under the impression that the video was supposed to lag, not the sound, when using digital video. I figured, "No problem", and went into the receiver setup and changed the delay from 20ms to 0ms. Everything looked great, but it started de-syncing again after a short amount of time. I double checked the delay on the receiver and all is still where I left it. So either a) I never fixed it and missed the smaller delay or b) something got confused again.
Also, I tried HDMI & SPDIF from my laptop w/ WinXP and there is no sync issues. Dunno if that's windows or the combination of digital inputs (rather than mixing digital vid and analog sound). I did notice, however, that the sound coming from the laptop speakers is out of sync (or Phase if you're a real audiophile) with the rest of the setup. Again, the 20ms or so delay.
I'd be interested in hearing which way it's desyncing for everyone else. Is the vid or sound faster? Also, what inputs everyone is using. I know some new devices have A/V sync controls (like my receiver).
For reference, my setup is:
HDMI vid card -> HDMI input on Onkyo Receiver -> HDMI input on Mitsubishi Projector
Stereo output on Hybrid Core -> stereo to RCA adapter -> receiver RCA L/R input -> speakers.
Hope this helped!