[rrival]

Take a look at what Revver has done with user accounts. Or Jellyfish.

There's usually a float involved which can be fun for cash flow (time between affiliate payout >= time your affiliates need to be paid).

Some companies won't let you / have rules about compensating users. For ex: WalMart doesn't like it, on the grounds that they feel their brand is strong enough to attract people without affiliates having to offer a monetary incentive.

[axod]

Float is good. Also usually the deal is "Minimum payout $20" for example.

Reward sites actually make most of their money by relying on the fact that most people earn a few rewards, give up, and never claim because they don't get to the minimum payout threshold.

Not a great business, but that's how that sort of thing works...