I saw Spinal Tap at Live Earth and was pretty impressed with them. This dvd is a lot of fun and completely takes the piss out of the rock music industry. Kind of like the Osbournes-back-in-1984.
However, it does get tedious after a while and I'm not entirely sure if I watched it through to the end or not. I wouldn't suggest people not watch it because of that - sometimes you're just not in the mood, you know? They were definitely brilliant in concert though.