I was at a Cubs game in 2004 and Katie Holmes' seats were a couple rows in front of mine. She had thrown out the first ball, and was on the field before the game. About the second inning there she was 2' in front of me in the aisle.
I've also briefly met a few sports personalities at various games or events: Bob Feller (HoF Pitcher), Hersey Hawkins (former NBA player), Elton Brand (NBA player).
I got an email reply once from Mark Cuban (owner of the Dallas Mavericks) from an email I had sent him concerning an appearance he made, if that counts.