Short answer: buy Bitcoin instead of mining.
The reason I selected this answer of buy Bitcoin instead of mining Bitcoin is because the current level of difficulty for mining Bitcoin will continue to rise and when BFL and KNCMiner and many other miners manufacturer shipped their 28nm mining hardware, the difficulty level to mine bitcoin will skyrocketed. Meaning it will be real difficult to mine Bitcoin. Therefore I think it is a lot better to buy Bitcoin directly instead of mining Bitcoin.
Mining Bitcoin with hardware you have onhand physically, you would need to set it up, and pay electric bill, and when it’s down you would need to fix it or RMA it. So it could be time consuming and stress. However if you’re into IT and want to learn, having one mining rig would be good enough, but managing a line of rigs might not be a good idea if you don’t have the time, such as family or a career.