Why do fingernails grow faster than toenails?
WAG.
The blood supply to the fingers is almost always better than the blood supply to the toes. The rate of nail growth may reflect this.
I’m speculating here but they may just appear to grow faster because toenails, being inside shoes a large proprtion of the time, are more prone to being worn by contact with the shoe.
Another top-of-the-head theory (since everybody else is doing it):
I suspect aramis has it backward. Fingernails are used a lot more than toenails, so they wear down faster. If they didn’t grow quickly, they’d soon be gone, which would be a big disadvantage in the wild, where our ancestors spent a lot of time digging up roots and bugs and things, and scratching their fleas.
Very clever. Teleology at its best (and I mean that in the nicest possible way).
Here’s my theory: they actually grow at the same rate, but we like our fingernails shorter than our toenails, so we cut the fingernails more, so it seems like they grow faster.
Another WAG:
I don’t know about the rest of you, but my guess is that both grow at the same speed. The difference? Your toenails are thicker (and the big one is wider), so it grows less in length, although both pump out the same amount of “nail stuff.” 
It seems to me that my right hand nails grow slightly faster than my left hand nails. Maybe it does have something to do with blood flow. I wonder if track runners’ toenails grow faster?
I’m a runner, but the only times I hit the track is when I do intervals. However, I have run 30 marathons and a 50-miler. My biggest problem with toenails is getting black ones.
But I also think they grow at the same rate. It seems like I’m cutting my toenails as often as I do my fingernails. And the toenails have to be cut down (and filed), else they grab onto the threads of running socks. Also they can rub against an adjacent toe and dig in, causing a cut.
I hate to be the one to point it out, but if you recall evolutionary theory, it does not create, only eliminate.
And it only eliminates things that reflect ultimately on reproduction. Since the growth rate of nails, either way, has little impact on reproductive capability, it’s unfettered.
No two things are exactly equal. They are nearly equal. Not fast-growing as those of some creatures, nor slow-growing as others. So the variation is more of an illusion, a statistical micro-view, that when viewed from a greater distance, disappears into the standard variation.
KarlGauss, I’m not talking teleology.
My speculation is based on the idea that having usable fingernails does have an effect on survival. Digging allows easier access to underground food, and scratching gets rid of parasites. Neither one is likely to have a large effect on survival, but even a small effect can accumulate over a few million years.