Well, dredging the old memory, when I was 13 Jimi Hendrix was doing a concert in my home town (Carlisle) and after hanging round the stage door for a while he came out and asked where the nearest Chinese was, so I grabbed one arm, my friend the other and we walked arm in arm to the restaurant! How cool was that
More recently (but still a long time ago) I stood beside George Best in Blushes wine bar on the King's Road.
Oh, and I nearly tripped over Wayne Sleep on Queensway.
Saw Paul Weller strolling round Covent Garden, saw John Cleese when I went to see Victoria Wood one night.
I have a feeling I've probably seen lots more round the streets of London, but I tend to think "they look familiar" but not being able to remember names!