Ask YC: Should I open source my product or not? (did you?)
xenoterracide.blogspot.com
xenoterracide.blogspot.com
I think in general people overestimate the value of their source code. There are so many other things that you can bring to a business that any copy-cats wouldn't necessarily have (e.g. your knowledge of the source code, your vision for the product, etc). So don't flatter yourself into thinking that as soon as you release the source, a dozen competitors will spring up using your software. And even if they do, you'll still likely out-compete them.
So like making any business decision, weigh the advantages and disadvantages of open sourcing and make a decision based on those. But don't make the common mistake of overestimating the disadvantages.