I suppose if I were going to be taxed because I'm overweight (according to the BMI) I might care a little more about those 5 extra pounds. But honestly, I'd probably focus more on finding a way to avoid paying the tax.
I love the BBC News site for this sort of thing, outrageous as it is. Just yesterday I discovered Ethical Man. Ethical Man's effort is a little like a one-man-band version of Morgan Spurlock's FX show, "30 Days." It's also a little bit like being the graduate of a certain small liberal arts college in Iowa, only with less emphasis on paper over plastic.