This feels like it gets asked quite often:

http://news.ycombinator.com/item?id=1734122

http://news.ycombinator.com/item?id=2891596

http://news.ycombinator.com/item?id=2848674

http://news.ycombinator.com/item?id=1525445 <-- has links to others threads on the same topic

It was a quick search and I am sure there are more that I missed.