Courtesy of Ausiello Files, Dexter's executive-producer Sara Colleton gave an insight into the writers' early discussion about what season 5 will involve, during an appearance at PaleyFest '10. Click the link for the full interview. But, as fair warning to British readers, there are monumentally big spoilers contained therein if you haven't seen season 4 (which you shouldn't have, because it starts on FX this summer.) I mean it. You'll be tearing your hair out if you click that link prematurely, so don't come crying to me! And if you want to leave a comment here about what's in store, please remember that comments get previewed in my blog's sidebar for awhile, so please try and dance around mentioning major spoilers for the first few sentences at least.
Update: E! Online tackle the same event in a more expansive way, with more quotes from the actors.