Deadline for registration is a postmark of this coming Tuesday, February 19th. Post offices are the easiest place to find a registration card, or you can print one out from the web at: http://www.ss.ca.gov/elections/english.pdf.
California is using a "modified closed primary system" this time around. What this basically means is that if a party has chosen to allow it, you can vote their ballot without being registered in the party. You need to be registered as a "decline to state" voter in order to do this. You also will have to vote their entire ballot; you cannot vote within different parties for different races.
According to the Secretary of State's site, the following parties have opted to allow decline to state voters to vote their ballots: American Independent, Democrats, Natural Law, & Republicans. To vote any other party's ballot you must be registered in that party, so if you wish to participate in the selection of the Green candidates, for instance, you need to be registered as a Green.
Also note that if a party fails to maintain at least 1% of the voting population (determined by the total voters in the previous election) or get a petition signed by 10% of the voting population, then they lose the ability to automatically place their candidates on the ballot. People registered in the Peace & Freedom Party or another low registration party may thus feel it is important to retain their registration in their party. Peace & Freedom currently doesn't meet either of the criteria and so must qualify each individual candidate by petition. Currently qualified parties in California are the four above, Green, and Reform.
The other thing to be aware about in this primary is that provisional ballots will supposedly be easier to get and have counted. Since the registration deadline is so close to voting day, it is very likely lots of last-minute registrations won't be reflected in the polling place lists. If denied because you're not on the list, or your registration hasn't been updated to reflect a new party affiliation or decline to state status, demand a provisional ballot. A photocopy of your new registration may help, although technically it has no meaning.
Patrick Ellis