I think he's been OK on taxes--not great. He didn't fight hard enough for the estate tax elimination and he didn't fight at all to eliminate our social security tax. Also: where was Bush & Co. on eliminating the AMT?
This, coupled with the ridiculous spending levels, is reason why I don't give Bush better marks on his tax policies.
Maybe I'm a bit biased since Bush tax cuts are one of the very few things done by politicians to ever have a good effect on my life. I also think that the concrete evidence that his tax cuts helped the economy will be a major asset to the anti-tax movement in the future.