No, I don't buy offsets. I think the idea of offsets is a great one, but I have no way of knowing if the money is being used for its intended purpose, how they are measuring the amount of the offset, or whether the project they invest in would have received funding otherwise. I also don't want to normalize the idea of pollution prevention to be voluntary.
I do, however, donate money to various environmental charities, both local ones in my community and a couple of the big national/global ones.