I wondered this too...
Since it sounds like a no, how often do they usually release beta updates? And what is the process of installing/updating them? I'd hate to have to do an entire backup/restore every time...
Over the past 3 years i have been installing the betas and this is what i remember, betas were released every 2-3 weeks and were almost always released released on Tuesdays, usually between 10am-6pm eastern time. Beta 3 is usually were the OS has most of the bugs worked out and any features that are supposed to be in the official released are put into beta 3 if they were not in the previous versions. Last year though there was a huge wait i think between beta 2 and 3(about 5 or 6 weeks i think) if i am remembering correctly.
This year may be different though as we are seemingly 4 months from the official release. In previous years the betas were released in mid to late April giving only 2 months worth of testing. The schedule now may spread out a lot more, maybe 1 beta per month depending on how things progress...