Haven't managed to be at any of Guy's panels yet, but I remember the first I ever saw him on, at the Worldcon in Brighton when the only thing he'd published was Fionnavar. You might have thought he'd take the opportunity to plug his own work (he had an hour-long talk to himself); but instead he spent the time speaking, with great emotion, about what it was like to meet Tolkien, and to co-edit 'The Silmarillion' and get to work with Tolkien's papers. One of the best author talks I've ever been to.

Have also had the opportunity to meet (for a brief moment) Geoff Ryman, who is to my mind one of the best sf/fantasy writers currently working. I always forget how tremendously tall he is - I felt like a little hobbit squeeing at an ent's feet :)