With the recent price surge of Bitcoin, I’ve been getting a few messages from people asking about the viability of building a GPU-based rig to mine bitcoins directly. Don’t do that! GPU mining is only suitable for scrypt-based cryptocurrency (Litecoin, etc).
If you’re interested in mining Bitcoin, then you absolutely must use ASIC hardware if you hope to turn a profit. For example, six of these will mine as many bitcoins as a full-size triple GPU rig, and they’ll do it at less than 10% of the cost and power consumption (remember to pick up a USB hub if you plan to run a few, and perhaps a small fan or two—they run fairly hot)!
The downside to ASIC-based mining is that the hardware cannot be re-purposed once it becomes obsolete—and with the rapidly-increasing Bitcoin mining difficulty, that will happen fairly quickly unless the price of the currency keeps pace. Remember that you can always mine scrypt-based coins with your GPUs and trade them for bitcoins on an exchange, as well.