Just a brief note on a short, relaxing trip - some of you may find it interesting.
My wife and I left our daughter with grandma and grandpa in the CA Gold Country and took off down to the SF area for a few days. We are very familiar with the area (I went to school at Berkeley), but we had never been to Half Moon Bay, so we decided to base out of there this time.
Day 1: Drive to Half Moon Bay, check out the town. It's a nice, laid-back town. Not over-touristed (like Carmel or Mendocino).
Day 2: Drive down the coast to Santa Cruz, stopping for sight-seeing along the way (the coast is gorgeous on this stretch!). Poke around the Beach and Boardwalk.
Day 3: Raining (pretty hard), so we went up to SF (about 45 minutes) and visited the Exploratorium. Tip for the Exploratorium: Come at around 2:00 to avoid the Field Trippers. This is a great place and you can spend several hours here - especially if you have a child in Jr. High with you.
Day 4: Walk down to the beach in the morning, then a leisurely drive back in the afternoon.
Highlights of the trip: Half Moon Bay itself, the Exploratorium, the Drive to Santa Cruz, the Flying Fish Grill in Half Moon Bay (excellent Fish Tacos)
Lowlight: the Santa Cruz Boardwalk (I just found it cheezy and loud)
Note: Half Moon Bay has no appreciable nightlife. That doesn't bother me - I am not much of a nightlife person - but if it is important to you, you should be aware of it.