At https://tipit.to/ we don't normally count pledges. We do display them, but in gray. Right now in our top charts I've turned on a little flag so that pledges are included in the front page top charts algorithm, but that's just for the launch. I'll turn that off sometime soon.
One of the main reasons we do this is because not counting pledges automatically reduces on welching. When an unpaid tip is something only you yourself can see, then there's absolutely no point in pledging a tip without any intention of paying it. The only welching going on would be those that honestly forgot. Either way, it doesn't drag down the validity and utility of the statistics.
Interesting. The other side of the coin is that encouraging people to click that button is the first step in getting real money. I don't think I could tell you which is a better idea without seeing stats for both, even then...
One of the main reasons we do this is because not counting pledges automatically reduces on welching. When an unpaid tip is something only you yourself can see, then there's absolutely no point in pledging a tip without any intention of paying it. The only welching going on would be those that honestly forgot. Either way, it doesn't drag down the validity and utility of the statistics.