The days of small miners making significant profits in pooled mining are probably coming to a close in a few years. The economies of scale and efficiency will soon take over.
It's sort of the same situation with gold mining. In 1849, you might be able to find gold nuggets in a creek in California and make a living at it. Now, modern gold mining involves strip mining a vein of dirt with a high enough concentration of gold to make it worthwhile to refine a dump-truck full of that dirt into a bar of gold.
Before you get started, use one of the bitcoin mining calculators to figure out your potential profit running a rig. The thing to keep in mind is that your average reward will decrease by 18% every two weeks, if the price of btc doesn't change. The last difficulty increase was 22%, which reflects the new mining technology coming online.
I did some calculations on my Antminer S1, and if the price of BTC remains the same, I have about 20 weeks until the price of electricity exceeds the mining rewards, assuming an 18% biweekly increase in difficulty.