I think the most recent time I've seen him was with his Big Band for the 80th Birthday gig. It was sublime, although he was a bit on the frail side - some fantastic new big band arrangements featured proving that his arranging gets better and better. Before that - a gig from the 75th Birthday Big Band with Norma Winstone and also around that time a concert with the group featuring Lee Konitz, John Taylor and John Abercrombie (I think). I also saw him about 15 years ago with Fred Hersch.
Oh - and a performance at NorthSea some years ago.
First time I saw him was with Azimuth plus Tony Coe back in the 1980s.