I started riding back in 1971, and Lane Splitting/Filtering (which are two different things) were practiced long before I started riding. Once I got my '72 Yamaha 250 twin, is when I started both. Once, I had filtered up to the front of a traffic light and before the light changed, a cop on a bike came up beside me, looked at me, knotted and took off. Before the law was passed, a few years ago, it really depended on the cop. Some didn't care, others gave you a warning! in the 49 1/2 years I was riding bikes in Kaliforniastan, I never got a ticket for either.
Now, here in Utah, it's a different story. You can filter up to the traffic light, on roads that the speed limit is up to 45mph and you are not doing more than 10 over.