Here's the text (verbatim) from the CHP's site: "Lane splitting by motorcycles is permissible under California law but must done in a safe and prudent manner." The text used to also include "The motorcycle should be traveling no more than 10 mph faster than surrounding traffic (without exceeding the speed limit) and not come close enough to that traffic to cause a collision." but has since been removed. Perhaps they wanted to give cops more latitude to interpret what they thought was safe so they removed it.
     If you lane split, avoid weaving between the two lanes and don't exceed traffic speed by more than 10 mph. The former could get you a ticket for changing lanes without signaling while the latter could get you a ticket for reckless driving.
     Your odds of getting ticketed also increase if you lane split between the carpool and fast lane. A double yellow line divides the two lanes and those are illegal to cross (with rare exceptions that would never occur on the freeway); I know of riders who have been specifically ticketed for crossing the double yellow while lane splitting between those lanes.
     Lane splitting on surface streets is probably not addressed in city or county laws so I would do this with caution, as individual cops will decide whether or not they like what they see. I split lanes on surface streets if I don't see any cops, but I stop immediately if I spot one.
     There's a little bit of information on "lane sharing" in the DMV Motorcycle handbook. They say to discourage its practice, but never say it's illegal.

Keep it upright and ride it like you mean it!