Yes, long-time CA resident drivers tend to expect lane sharing/filtering, especially in the heavy traffic-prone metro areas. However, aside from the typical cell phone-distracted drivers, perhaps the biggest wildcard for a filtering motorcyclist is the high percentage of drivers in CA who aren't from CA, such as nervous, confused, lost, scared, distracted, oblivious tourists from all over the world, and for that matter, a not insignificant number of unlicensed and uninsured illegals behind the wheel. In my experience, some tourists are highly unpredictable behind the wheel, so I have learned to give obvious rental cars and those with out of state plates an especially wide berth when I'm on the scooter in CA. The most touristy areas also tend to be the most likely to have heavy traffic with filtering bikes, such as the LA and SF metro areas. As was pointed out, sometimes the risk of NOT filtering forward outweighs the dangers of carefully doing so, but you're putting a lot of trust in the drivers around you no matter how good you are.
I also agree with what was said above and in the report about HOW you filter being perhaps the most critical factor. It makes me cringe to see bikes lane splitting at full freeway speeds, or passing between stopped or slowly moving trucks and cars at speeds far in excess of the traffic around them. They are leaving themselves little to no reaction time and not giving the other vehicle drivers a chance to see them coming. I watch for filtering bikes when stopped in traffic, of course, but I have been caught by surprise many times by bikes coming by me so fast I neither saw nor heard them until they whizzed past my ear.
It's especially dangerous around vehicles with significant blind spots, such as trucks, buses, and RVs. I recently read a report of a freeway crash in CA where a filtering rider ricocheted off the side of another vehicle in traffic and careened under the trailer of a semi truck that was slowly moving forward in the next lane. The truck driver apparently didn't notice the bike coming nor the ricochet that sent the rider to the pavement under his trailer. His trailer wheels ran over the downed rider, with fatal results.
As a defensive riding technique, I have made a mental practice of PLANNING to lane share even when I don't intend to, and even in places where it's technically illegal. When traffic starts slowing down, I try to keep my distance from the vehicle in front of me in order to keep my options open, pick my escape route, keep rolling along in 1st gear if possible or stay in 1st gear if stopped, and watch my mirrors closely. If things look bad behind me I'm not going to just sit there and get blasted, I'll be lane splitting like a crazy man.
! I love my modualtor too. I find that it helps a lot to get drivers out of my path before I get there. 
