Is there really any point in joinin a "rig" if you ca just buy bitcoins from an exchange anyway?
It's called a pool, but there's probably no point for the casual miner at this stage.
OK, you may get 1 BTC a day for free if you're lucky, probably more like 1 BTC a week very shortly because of the mining competition increase, but it probably makes more sense to buy 1000 bitcoins at $10 each and resell them when they reach $20/BTC.
That's assuming the exchange rate will increase, which is likely in the medium term, but now the American government is looking at the bitcoin system, so I would not keep bitcoins on the long term. I know, "they'll never be able to shut us down etc."
If you make enough money buying and selling bitcoins to pay for a mining machine, like a $3000 PC with 3 Radeon 6990 cards that mines at 2 gigahashes/second, or even a less ambitious system, then it's a different matter, because you basically got it for free and can resell it for real money if you need to. Just don't expect a mining machine bought now to pay for itself any time soon. Still, for the gamer, you get a great machine at reduced price.