Do you mean if you raise say 4BB, they make it 8BB - or that they raise an unraised pot to 2BB?
They raise an unraised pot to two BB.

I'd say roughly half of the time a random utg minraiser will have a monster hand, while the other half of the time it represents a marginally strong hand.
Yeah, this actually seems right. I guess it just always stands out when people do it. I will say that on Bodog it might be more like 75% of the time--I need to take a break from that site, it's skewing my poker worldview...