My XBox came with just the plain, old composite AV cable (not HDMI), so that part of the audio delay issue was resolved for me. I never had an HDMI output from my XBox console to cause a delay. Still, the latency issue in my setup was so bad that we pretty much abandoned Rocksmith for a week or so. It was just unplayable.
Fortunately, this is really easy to fix. In a perfect world, you could buy Rocksmith, load it on your XBox (or whatever console you have), plug in a guitar and go to town. But, it would appear that this latency issue is unavoidable. It's just physics; electrons can only move so fast and sound is slower than light. That's just how it is. The audio output is addressed right in the "game," so I have no beef with Ubisoft/Rocksmith about this and neither should you. They could perhaps include some actual written documentation with Rocksmith that explains this and includes some specific setup tips, but apparently I'm the last person in the world who still prefers hardcopy manuals/directions over "readme" files and online help.
After consulting the many forums already addressing this issue, I tried a few of the most commonly posted solutions, including setting my TV to "game mode" or the closest audio setting I could find in the setup menu. My Hitachi LCD TV doesn't really have a "game" setting for audio, and my next best guess at the equivalent setting didn't really help the audio latency issue at all. I was a bit discouraged at that point, but I still had the option of running my audio out to some computer speakers.
Instead of doing that, I replaced my already dead home theatre receiver with a new one and ran my XBox outputs - all of them - through that. I fully expected that the delay might actually become worse. But, using no effects and just the regular stereo setting got Rocksmith working great. There is probably still some latency because it simply takes a certain amount of time for the electrons to get from my guitar pickups to my TV screen after passing through all those wires, cables, the XBox console, and an amplifier (not to mention the time it takes vibrations to get from my guitar string to the pickups). But, humans perceive anything which happens in less than about .3 seconds as "instant," so I'd say I've got my electron travel time down below .3 seconds. If I've got some latency left in my setup, I can't tell it. And, based on the dramatic improvement in my scores, neither can Rocksmith.
Probably due to the specific model and make of receiver, I also had to run a composite video (RCA) cable from my receiver's video output to the TV even though I have an HDMI cable running from the receiver to the TV for everything else. Apparently my receiver is not able to upconvert an analog composite signal to HDMI, so any analog inputs to the receiver require an analog output to the TV. No biggie. Just something to be aware of.
So, we're back to thinking Rocksmith is the greatest thing since sliced bread. I've got 70,000+ on at least a couple of songs so far and the blisters on my fingertips to show for it! So, now I guess I'll join in the nationwide snivel-fest over what songs should be included next. My vote would be for some Eagles (specifically Hotel California and Life in the Fast Lane) and possibly some Pink Floyd. But, it's not like I've mastered any of the songs that came with the original release, so no rush!