Entrants as of December 2, 2008, 7:36 PM EST:
HALF: 293
FULL: 285
I believe I saw that they were capping it at 750 athletes in each (1500 total), if I'm not mistaken.
Full - 317 registrants
Half - 348 registrants
If they cap it at 1500 total (750 each) like they indicated, that looks to me like it's 44.3% full.
Update: December 31st, 2008:
Half - 412 registrants
Full - 365 registrants
51.8% full
Update update: January 8, 2008:
Half - 492 registrants (65% full)
Full - 392 registrants (52% full)
Update update update: March 3, 2008 (69% full overall):
Half - 588 registrants (78% full)
Full - 442 registrants (59% full)