I found this in the FAQ on the Rocksmith site about latency... maybe helpful for some people who have the talked about options on their TV:
If you experience any noticeable latency with Rocksmith, then it’s more than likely due to the specific setup you’re using. Since everyone has a unique arrangement with their home entertainment systems, we’ve outlined steps you can take to avoid this issue.
If available on your TV, use the "Game" or "PC" mode setting. These modes bypass extra video processing filters to seriously reduce lag time.
If the TV does not have a Game or PC mode, you can diminish lag by turning off video processing filters. Refer to your TV manual for more information on how to turn off processing filters.
Check to see that the console is outputting video at the native resolution of your TV. If your TV’s native resolution is 1080p but your console is set to 720p, the TV must process the signal to scale the image up to fill the entire screen, which adds to the input lag.
On some TVs, HDMI connections can introduce more input lag than component or PC cables. If your TV has noticeable input lag using HDMI connection, you can diminish the lag by switching to component video cables or PC cables.
If you’re using external speakers, connecting the audio from the console to a stereo receiver or home theater system using analog audio cables can fix audio lag. To match the on-screen note display to the audio, you can advance the notes using the "Note Advance" calibration.
here is a pic they give of setups:
http://rocksmith.ubi.com/rocksmith/en-US/setup/index.aspx My wife wants it for x-mas, but I think I'm going to wait for the PC version and see how bad everyone says the latency is, plus I'll still be able to game on the xbox if she wants to play this for hours on end, not to say I won't be playing it also.
The track list with the game isn't really that appealing... future DLC $$$