What do polls mean?

I didn't put a lot of meaning in polls when it was Bush, and I still don't put a lot of meaning into polls. People will throw this data around like it is some kind of concrete fact, but it isn't. Or it is a fact, but I think it speaks very little to reality.

clipped from hotair.com Give Rasmussen a lot of credit thus far in the Obama Era.  They predicted his decline first, have documented his rallies, and now report on the nadir of his standing among registered voters.  In their daily tracking poll, Barack Obama dropped to a 45% approval rating, tying the lowest mark of his term thus far, and hit a new record on their “passion index”