Never one to settle for just one record, US GM Susan Polgar seems to have broken quite a few during her marathon simul in Palm Beach Gardens. The main one is the most games going at the same time, which she has pushed up to 326. (If you wonder why people don't do this sort of thing often it's because it's hard to get opponents to stick around. Even at brisk five seconds per move that's still almost half an hour between visits to your board!)
The level of opposition isn't really the point of these things, so getting into wins and win percentages seems a bit silly. It's a feat of endurance and PR for the game and her foundation, and certainly a considerable one in all categories. It lasted 17 hours, 1,131 games, and required walking about a marathon's worth of distance (well, nine miles actually). (In 1984, Hort played a total of 663 games in a simul in Germany that lasted over 32 hours. Nobody sane will ever break that record. (Several people have reminded me that Gideon Stahlberg did 400 games in 40 hours in 1940. This was on the same list I checked for the Hort record but somehow my brain didn't digest it.) It has gotten good AP coverage, though the Washington Post is one of the few to run a pic so far. There is now a pictorial report up at ChessBase.com.
Susan Polgar has posted a long note in another thread.