Float is how American Express made its profits in its early days. You would buy AmEx Travellers Cheques, and then days or weeks later use them for payment. In the meantime, AmEx got paid twice: once, when you paid a fee to buy the cheques, and then again from investing your cash until it had to pay the merchant (and perhaps earning a third fee?).
I wonder how much profit Google makes from float? That's the money it earns from advertisers, but doesn't pay out to us until our accounts have at least $100 in them. I make more than $100 each month from AdSense, so there isn't much float there.
But after 1.5 years in Goggle's Book Search Partner Program, I've made just $17.92 -- which means I can expect to be paid after about ten years. By then, they'll have raised the limit to $200, and I'll have to wait another ten years, and on it goes.
I am guessing that Google needs to set aside that $17.92 for accounting purposes. But in the meantime, it can invest the float, and profit from the investment. Google pays me no interest for my cash that it keeps from me.
Multiply $17.92 by thousands (millions?) of under-$100 accounts, and suddenly we're talking real money -- some of which Google might never pay out. I haven't read anywhere anyone wondering about the size of Google's float. But it struck home when I read a blogger complaining of never being paid by Google, because over the years they kept raising the payout bar on her.
Perhaps someone might want to take up the task of calculating how much of Google's financial power comes from cleverly employing its customers' float. I wonder if Google sets the payout limit on the basis of how much float they need?