I would also like to add, the first time I visited California and saw someone lane splitting, I thought they must have been running from the cops. I can't believe it's legal... and I live in a state with no helmet law.
Everywhere in the world where motorcycles are ridden in traffic, almost without exception, lane splitting is not only legal, it is absolutely normal. One of the few exceptions is most states in the United States, and I thank whatever supreme being you choose that California is not one of them. For as long as I can remember, riding on two wheels has been my preferred mode of transportation starting with the first bicycle from which dad refused to remove the training wheels, so I did it myself (lifelong mechanic as well!) at the age of 3 1/2, and finding that dangerous tip over prone monster suddenly made sense. You couldn't get me off it! Fast (yeah, lots of it) forward to 1970 and my first freeway legal motorcycle, a CB 350, which brought a revelation: lane splitting! I would intentionally go on rides during rush hour just to practice, and found not only that I was pretty good at it, but the intense concentration required was almost addictive -- you are definitely not thinking about anything else! Being absolutely in the moment, the hundreds of decisions per minute required, watching the dynamic of traffic flow, reading the intent of drivers sometimes before they know themselves, and being very well trained in the finer points of control of your motorcycle and how to put it exactly where you want it at any given moment, are just a few of the benefits of splitting -- well, that and getting where you wanted to go a hell of a lot faster. Personally, I know I'm a much better rider due in large part to the education I've received in the classroom of the jammed up freeway, and doubt if I would be as enthusiastic about riding if splitting were illegal.
Two quick examples of normal splitting: moving along about 15 to 20 MPH faster than traffic, came upon a gap to my right, which incidentally sets off alarm bells, and sure enough the car to my left makes a dive for it ... quick flick to the right just past the front bumper of that plumber's van, a small twist of the throttle to gain room, cutting left to skirt the far line and noticing the car has cut back into the fast lane, two fast downshifts while cutting back left to hit the gap ahead and giving a friendly wave (All five fingers, thank you! He noticed me and I appreciate it.), and put my hand back on the bar just in time to miss the mirror on my left. All in just over two seconds.
And my favorite maneuver: getting to the front of a red light, I'm blocked three cars ahead, so steer between two cars to the next lane over, get past the block and repeat in the other direction at about 2 MPH. Believe it or not, I got applause from a CHP motor officer who saw one of those.
So splitting can be potentially deadly or as safe as anything you do on a bike, it just depends on your skill and judgement.
Oh, yeah -- I'm planning a pair of narrow lane splitter / urban commute bars welded up in .083 wall seamless 316 stainless. Get back to you on them.