I have been there. Not bad for a big venue, although I prefer a more intimate setting. I saw the Verve, and took the wife to see Enrique Iglesius. Seeing the Stereophonics and Bon Jovi there next year too.
We get in VIP into a corporate box as my company has a big contract with O2.
This is V cool. Not sure about the normal seating, but my mate was up the top once with the pigeons during the Verve and he said he was scared of the height.