Gotta disagree here. Splitting lanes in CA I had cars on an almost daily basis, see me moving up trough traffic, and purposely move their car over onto the lane lines to prevent me from splitting on a freeway or up to the front at a red light.
In CA, you're only supossed to go 15 mph or less faster than traffic is moving. Unfortunately, many squids blow down between lanes at high speed, freaking out cage drivers, and generally making people hate the splitters.
On the other hand, I had many guys in trucks move over a bit in their lane when they saw me, so I could get by their mirrors. My guess is that these guys are riders themselves or wish they were.
IMO lane splitting is a great time saver. My commute from Newport Beach to Riverside could easily be 2 -2.5 hours in the cage (with an $5-9 toll road short cut), on the bike it was maybe 1.5 hours (with free tolls, depending on the route). Difference is, when I got home I was exhausted. Splitting lanes takes 150% concentration if you dont want to get squished.