Yeah, you could use it for a sense of trending, but not for a sense of a true baseline.
And in addition to trending, it is probably indicative of intensity too. Hard to believe that Cain is 3 to 1 favorite over anyone else among caucus goers, but not hard to believe Cain’s folks are really fired up at the moment — so that they will make sure they go to the poll site and register their opinion. I would imagine a surge for Bachmann in this next poll from this group and would think Newt would disappear, unless his 3 remaining supporters spam the poll somehow.
But this is good also, since intensity leads to fund raising and yard signs and bumper stickers and neighbor chats.