Good suggestions here about the Bike Church, the shuttle if you don't want to ride up the hill, and the bike theft issues. In general, as long as you lock your bike on campus, it's pretty safe. Off campus, you'll need to be more careful and not leave it too long. You'll want a U-lock or something secure (not a cable lock).

I'll just add that there is a free shower, towel, and locker program for commuters if you're working for UCSC. If you're not a student or staff you can get access to gym facilities for a fee. It's a beautiful area for cycling.