We opted out at the hospital (and again at the 1 & 2 month visits). As PP's have mentioned, it's an STD - it's pretty ridiculous to vaccinate LO if no one in your family is a carrier. I'm a SAHM and LO isn't going to day care - his risks of contracting Hep B are basically 0.
We are on a delayed vaccine schedule and will get ALL CDC vaccines (including Hep B) before he starts elementary school. We just don't feel the need to rush the lower risk ones (Hep B in particular) at this time.
I'm not actually in the vaccines cause autism camp, however studies like this one about the Hep B in particular aren't encouraging