Just to give you some stats on what Im getting and have found out.
My gpu's pull 350 megahash each(idk what a hash is, but its the calculation speed I assume)
I joined a pool, which is several hundred users working towards the same block, every block has 50 bitcoins, but it is unknown how long it will take to solve a block.
A commonly used analogy is rolling dice. Imagine you have x number of dice(x being the difficulty) and a rolling for a specific combination of those dice. Your gpu rolls 1000's of times a second, and it could roll the specific combination in 1 roll, or ten years worth of rolls(wont happen but you know how probability works, you theoretically "could" flp a coin a million times and have it always come up heads)
When the block is solved, the pool manager keeps 0.5 bitcoins for maintenance , and the other 49.5 are distrubuted According to the % of work you put forth to solving the block. I currently am #25 in my pool, and get around 0.35 BTC for every solved block. Usually 1-2 are solved over a 24 hour period. The current market rate for a bitcoin is around 15$.
At that rate I am making roughly 10$ a day, but if you look at how WILDLY the bitcoin market fluctuates, there is great chance that 1 BTC could become worth 100 USD in the coming years.(Also great chance of it being worth 0 usd unfortunately)
I have found many places to legitamately exchange bitcoins for cold hard cash, prepaid debit cards, or goods.
I have personally bought a real life bitcoin(no value, just for looks) Plated in gold(brass) Of very nice quality for 0.59 BTC, so I can attest that you can at least do that with them.
There are currently 710.3946 BTC in demand worth an estimated 12,493 dollars.
There are many users who buy POS cheap ass mobo's with a ton of pci-e slots and build minimalist rigs with top end gpus, hooked up vie PCI-E extender cables, so that heat becomes less of a problem from stacking. Heat is also counteracted by SEVERELY underclocking the GPU memory. They underclock like many people overclock, finding the highest core to lowest memory ratio that runs stable.
One guy in my pool currently draws 12-15 ghash... I get 1.2 ghash max. He has apparently built a massive mining farm and invested a lot of resource in the Bitcoin craze. He gets around 3-3.5 bitcoins per block, which translates to roughly 100$ a day at current difficulty and market rates.
Just a bit of info I have found on the subject for you guys.