The amount of processing power you need to mine bitcoins keeps going up, it's
the nature of the beast. On top of that, the companies making dedicated bitcoin miners
are untested, and there have been complaints. Really ought to build your own.
The demand for processing power has driven up the price of Radeon cards, which
means something that will actually be strong enough to make money will cost you
thousands (cards strong enough are several hundred, and you really ought to get the ones
that are a grand EACH). Expect a big jump in your light bill...
It is possible to make money, but your superfantastic bitcoin miner is not a long term
investment, they get obsolete fast. Between the cost, the risk, and the whole DIY
thing (which I'm not good at) I don't think it's worth it. Money works only if people believe
it's money. It wouldn't take a lot more bad news to bring that to a messy end.