Matt Asay has an interesting blog post about how open source software bugs get squashed faster.   I'd like to add that it's not that they get fixed faster, it's that the fix gets out to end users faster.  An open source fix is available to end users almost immediately after it gets created.  With almost any proprietary software the company has a whole test and QA process that needs to be followed first and it's at least days if not weeks before the fix is released to end users.  

I'd take it one step further and say that's why security is so much better with open source software.  When there's a security flaw in open source software, there's a fix released immediately.  With proprietary software, they try to keep the security hole quiet until they publish their fix, which just by the nature of their processes takes longer than the release of an open source software security patch.   The big proprietary company guy that finds the bug in the middle of the night is not allowed to publish his fix – he needs approval from others.  In the open source world, he can publish the fix right away and others can begin reviewing and commenting.