clipped from chessbase.com

Susan Polgar world simultaneous chess record attempt
31.07.2005 – On August 1–2 there will be an attempt to break the record for the greatest number of chess games played simultaneously, as recorded by the Guinness Book of World Records. The simultaneous master is GM Susan Polgar, who will attempt to play 350 opponents at the same time, in a 24-hour period of time. Pictures of the preparation.

The previous record, as far as we know, is 321 games played by IM Andrew Martin
(of ChessBase
DVD fame) on February 21, 2004 at the Wellington College Crowthorne. Earlier
records were 310 games played in 1996 by Swedish GM Ulf Andersson (result:
+268 =40 –2, achieved in 15 hours 23 minutes).

A simultaneous exhibition given by Samuel Rosenthal in Paris in 1867