I was contacted by a woman at SamTrans about the special service they plan to provide on Bay to Breakers day (May 18, 2008). Here are the broad strokes:
In order to facilitate the transportation for runners and fans there will be strategic locations throughout the San Mateo County to board an express service. The drop off will be close to the start line and after the race everybody will board close to the end line to come back to San Mateo County.
This will be a great service and no need to worry about arranging transportation or parking. Just like last year, SamTrans will also have one of the buses available to hold extra clothes and food (no valuables). The whole service will cost only $8.00 ($4 each way).