i saw him play 3 times (2003, 2004, and 2005) at the Siebel Open in San Jose- I was supposed to see him this year until he pulled out last minute. The first year he won the title match incredibly easily, so it wasn't that amazing to watch (he didn't have to pull out great tennis to win, but it was still nice to see him dominating). The next two years he lost before getting to finals, and he was playing really poorly (you know how once he's irritated, he often starts making a lot of double faults, stupid errors, etc?) everyone was really confused/ it was sad to see him in that state.. i'm still hoping to somehow get a chance to see him play at the quality the people above described!
i've seen him up close as well, and he does look pretty small/compact in person.