I've read that it should generally be 1.5x the amount of memory you have, but since I just got my second order of ram in, bringing me to 16gb, having a 16gb+ swap file would be kind of outrageous. A few forums that I've looked over seemed to agree that after 4gb, having a PF of 2gb is plenty, while other people seem to think <512 is fine.
Then there are the people that say disabling it poses no problems. In fact, Aldius, who I talk to regularly, says his is disabled and he has no problems at all and he runs 8gb.
I've set mine to 512 for now, but would like to know what you all do with yours.