For John Mayer's Battle Studies Tour 2010, the Nikon 70-200mm f/2.8 proved to be the perfect lens on the Nikon D3.
With John Mayer set back roughly two meters from the edge of the 5-foot high stage, I found that the Nikon D3 and 70-200mm f/2.8 were the perfect lens for this concert.
Light levels were generally quite good, with plenty of light to shoot at ISO 1600 with no real concern about shutter speed. I think it would have been possible to shoot at ISO 800, too, with ease, but the image quality at ISO 1600 is so good on the D3 and D700 that I didn't worry about it.
John Mayer doesn't move around too much on stage due to his vocal duties, and even his guitar solos took place mostly at or around the mic. The few times he did move to the front of the stage, there was oddly only atmospheric lighting – no spots or any other appreciable front lighting.
Overall, lots of backlighting and opportunities for flare, but also a nice, leisurely shoot of three songs.
For me, one thing to always consider when photographing John Mayer is his guitar faces. I think he ranks right up there (but probably slightly below) Dave Matthews for the myriad faces he pulls.