It won't be realistic to short FB in the first few weeks. Shorting is dependent on someone lending you shares, and that will cost some absurd fees in the immediate future.
Update: Per this article, the option market will start 6 days after the Facebook IPO:
http://online.barrons.com/article/SB500014240527487039645045...
(From some long-ago memory about other IPOs, I had thought it would be weeks or even a few months.)