I recall hearing a presentation by a representative from Polaroid who had been involved in some film testing in Polaroid's laboratory. He said that Polaroid's testing of CONVENTIONAL films indicated that freezing in fact retarded, if not completely supressed, the natural aging process of film. Therefore, he concluded that stocking up and freezing film does make sense.
However, he also noted that when frozen film thaws, the aging process resumes - and that Polaroid's testing showed that it actually accelerated. His conclusion was that film that had been frozen and thawed should be used and processed as quickly as possible.
Several other responses commented on the issues involved in thawing frozen film - that it most thaw completely, and that this takes several hours (I have always allowed overnight), and that the film packaging should not be opened until after the film fully thaws in order to avoid condensation on the surface of the film.