I'm not at Monitor, but I'll throw in my tuppence since noone else is.
1) Probably London, as the principal European office (the second biggest in the whole group)
2) No idea - they're not that big, so it'll be ad-hoc I expect
3) No idea
4) The offices they have have been established a while, but there don't seem to be any expansion plans afoot and most people in industry (clientside) haven't heard of them on this side of the Atlantic.
5) No personal experience, but the Vault 2006 survey covered "quality of life" in detail for 31 firms including Monitor. In the top ten for work/life balance, BCG came 5th, Bain came 6th, Marakon came 8th, but Monitor didn't figure at all. Gallup Consulting came 1st and Accenture came 10th, for comparison.