Red Octane has certainly been keeping up with the times and has heard our respective cries for help. In addition to supporting Widescreen and Progressive scan output, there is a feature in the video options which allows you to calibrate your HDTV Lag such that a delay will not affect your Guitar Hero experience.
So, for all those folks looking for an accurate way to measure the input lag on a new HDTV set or on the HDTV you already own, I highly recommend a purchase of Guitar Hero II. The game is released officially on Wednesday, but some retailers have already broken the street date (read: Wal-Mart) so a few lucky souls may be able to pick the game up already.
The game uses milliseconds to measure rather than frames. For reference,
1 frame is approximately 17ms (assuming the game runs at 60fps).
Please take my recommendation and purchase Guitar Hero II if not for this feature alone. It's also an awesome game, so it's win-win.