Personally, I would never recommend riding a turn lane or a not bike legal lane for a split. The more outside the law you ride, the less predictable and more of a distraction you are to other drivers. While it's legal here, I generally do it sparingly when I feel totally comfortable that I can pull it off without incident. Generally I only do it:
A) At a red light when there is a considerably large gap and the mirrors of any set of cars aren't lined up.
B) When I'm on a freeway parking lot or heavy uphill traffic (Although, I won't go over 25 mph along near stopped traffic, but I usually take it slower than that. I'll admittedly take bigger risks if it means not stopping on a decently steep hill, however).
C) When I can see that perfect gap, I'm going fast enough that the cars in front of me won't have time to alter their path of travel before I'm already done, and I'm feeling a bit hell bent ^^;
As I do it more and more it becomes much easier and my restrictions become a bit more lax. Just like anything, practice makes perfect. Just trust your judgment, stay in your comfort zone, and keep a careful eye on the vehicles around you, and you'll be fine.
On that note, it's really interesting to see how some cars react to lane splitting though. Most don't actually do anything physically, but I've had some cars move further out of the way (which I don't mind), and some cars move in closer to the car next to them so I can't get past them (which is rather irritating- even if I do understand their jealousy
). It's definitely adds that much more risk to riding at times, but the time I save, getting to leave some of the likely dumb as hell drivers behind me, and the rush I get from a clean split all makes it worthwhile.