The only problem really I forsee with legalizing pot and trying to keep it out of drivers hands, its very difficult to test to see if someone is actually "high or impaired" really all you could do is test and see if they could actually "drive" IE walk a straight line hop on one foot.
This is simply on the grounds that THC is a naturally occuring chemical its in your food just in loow doses so unlike booze your body doesn't react negatively to it and doesn't attempt to flush it from your system, so a blood test would only prove that you've smoked pot in the last month =/ not smoked and then hopped in your car.

But otherwise yah, I think it would help the goverment funding scene out ALOT if we stopped trying to prevent it and just taxed it!