Ever wondered why you seem to do worse in games when playing on your fancy new HDTV? Don't second guess your skills just yet - you may have a case of "HDTV Processing Lag."
Luckily for you, Hypercombofinish has posted an excellent primer on just what causes the issue, what it means for your gaming experience and what (if anything) you can do to alleviate the problem.
In a nutshell HDTV Processing Lag is a problem caused by the way electronics manufacturers craft high-end modern televisions. In an effort to make the picture that much more crisp and gorgeous, these firms have added a number of visual filters to their sets that cause a minuscule amount of delay between the input signal and what the TV actually displays.
This isn't a problem when you're watching something like a DVD. As long as the television in question adds a 300 millisecond delay to every part of the film, the entire thing appears to be playing as it should.
Gaming however is a different beast, and since you're constantly feeding new input to your console, and thus the TV, the delay can become quite noticeable -- particularly in games that require extreme precision such as Guitar Hero and Rock Band.
Interestingly, the less advanced CRT televisions of old didn't have this issue as they were able to display an image instantaneously, without having to add any sort of graphical trickery.
As Hypercombofinish points out, it is possible to calibrate certain games to make up for the lag, but there's no foolproof way to get rid of the problem entirely.