It's not what you think. Perverts!
I stuck on Hutchinson yesterday, late afternoon, going back to Queens from my upstate riding. It poured like there was no tomorrow, and cars were crawling. I've never split lanes in such weather and witch such low margin of error. But my left hand was killing me - and that's with hydraulic clutch.
On a side note, if you saw a tornado warnings yesterday, that's because I was going so fast through upsate NY, in circles - like the superman.
I also now know that the gravel is worse than the wet tar snakes.
Yeah, and about the lane splitting etiquette - there isn't one. Just do it expecting an asshole once in a while. Actually, number of cars moved to the side to let me go through, and I always say thanks - either nod of the head, or a wave if I can take that tired left hand off the handlebar.