I suppose that I should have done this for the last poll when I took it down, but the results weren't very interesting: nearly everyone used AGS forums.
Anyway, this last poll (Which version of AGS do you use?) was a bit more interesting. One person registered as using AGS 2.62 (last DOS engine - probably either Yahtzee or Gilbot!) and 5 people (10%) said they don't use AGS (wow, I'm flattered that you're reading my blog!) . Of those that use AGS, its pretty much one thrid each to 2.72, 3.0 and the latest beta (now 3.01, I guess).
Now that 3.01 is officially out, I don't think there's any gotchas in upgrading, so probably 3.0 will fade out (as have 2.70 and 2.71). But probably most of the people on the 3.01 beta will move to the 3.02 beta (or whatever CJ comes up with next) as they are "early adopter"-type-people.
And I guess gradually 2.72 users may slowly move over to the latest 3-series version, but its a quite a bit of an interface change so that will occur more slowly. There's also a thread discussing versions used in the AGS Forums.