I took some with flash and some without, I think all 4 of these are flash, came back from the gig with 1014 shots (hmmmm) 35-50% worked so that itsn't bad, although I am not judging in the same way I would with a landscape. Concerts and gigs are always tricky. Its hard to get a good position with monitors mic stands and all the usual stuff you find on stage. The lighting can be horrible, but it can add so much to the feel of a shot that I always try to get a few without flash (or shoot 2 or 3 in a burst as the 2nd won't have full flash power and the 3rd non at all). I have a bit of a reputation now locally that allows me more freedom at local events, so I managed to wheedle my way into the orchestra pit and spent a lot of time stage front with my head in the PA system. This is the first time I have used the D2x with a full stage lighting and it handled itself well, a couple of issues with strongly backlit focussing but on the whole well impressed.
Thanks for the nice words.