Jon,
I just flew through the SFO Class B (with clearance
) yesterday, heading into San Carlos (KSQL). There were actually 3 RVs on the frequency, one of whom I chased all the way into SQL (we met and chatted on the ground).
My experience has been similar to the others. Call ATC early, sound professional (I give a courtesy call with "position, altitude, with request", and then make your request (in my case, "VFR flight following direct San Carlos, Class Bravo clearance"). That's just one example call.
Getting clearance into San Fransisco and San Diego Class B has been easier than getting an LA Class B clearance in my experience. Down in LA, I've almost always been told I had to transition via one of the VFR corridors, so I normally go over or around. Leaving OSH headed south then east, I stayed clear of the Chicago Class B (around then above), but used Flight Following, as I fly through there a lot at work, and know how busy Chigago's airspace is. I'd be interested to hear if folks get Chicago Class B clearances easily. Atlanta and Dallas are what I'd call very busy Class Bs too, and it sounds like it just depends (good to hear the experiences there, for future use!)
It can be done, just be on your game. Yesterday, when I first checked in, after a few minutes I was asked to do a 360 because of crossing Osprey traffic out of Travis AFB (first time I've seen one in flight). Then on the next freq, as I descended towards SQL, still staying under Class B, but with the lower sectors looming up fast, I had to gently nudge the controller about my Class B clearance (she was busy with other aircraft). Got the clearance just before I would have turned to parallel the lower boundary, and pressed on. Just know where ya are!
Worked out pretty slick, getting to go direct!!
Cheers,
Bob