The official word:
http://www.pdga.com/files/documents/09PlayerDivisionsGrid_0.pdf
Basically, above 935 you play either Pro or Advanced Am.
900 - 935: Intermediate
850 - 900: Recreational
< 850: Novice
Of course, it's up to the TD how to enforce that in non-sanctioned events. And not every division is offered in every event. I'm taking my pathetic 828 rating out this weekend and playing in Rec, as there's no Novice division on offer. I'm also chuckling to myself that there's one 893 rated player in Rec, which while legitimately within the guidelines, is higher than 2/3 of the Intermediate field, and at least 54 points higher than the next highest rated player in the Rec field. I'm thinking of taking him some canvas and sand as a joke.