When commuting, the only times I use a rain jacket is when it is also pretty cold. I tend to heat up very quickly---then overheat, so I just wear a few layers (Capilene or Polypro). My commute is only 7 miles so I can usually gut it out. I do use booties, though.

On longer rides, I will carry a rain jacket, but use it only if the rain is heavy or if I need to heat up inside it (doesn't take long).

Seattle is a great place to ride--in city or out in the foothills.
Let us know when you're here.

Peace in the pedals!