I've heard the phrase "With a thousand eyes, all defects are shallow", so many times that if I ever did once know who exactly coined it, it is a certanty I can't possibly know now, however the top two contenders for this prize are Linus Torvalds, and Richard M. Stallman. The thousand eyes effect is simply this, with Open Source, since anyone who want's to look at the code, and or try their hand at modifying it, gets to. Opinions aside, and programmers are an opinionated lot, if you were looking at a mistake that someone made, you stand to become "Good Guy" famous if you report it to them. Err well at least in the Geek world you'd be famous for a day. Now multiply that effort times all the talented people who use, and love Linux and you start to wonder how any bug could ever slip through. But slip through they do. People who make a living spreading FUD,(Fear Uncertainty and Doubt) attempting to derail Linux or at least slow it down, so that certain for profit software makers remain totally unchallenged in the market place, are the first to point out what they call the Thousand Eyes Fallacy. On the face of it it looks like a pretty good machanism to catch a lot of bugs for free, and yours truly has spotted a bug or two, and sent E-mail back to the author, I even went so far as to point out the rather obvious fix, and I've had folks spot bugs in my code, so it works.
But you can't expect something like that to get every single one, there will never be the day that any nontrivial program comes out completely bug free. However contrast that with Closed Source code, where such world wide feedback is, due to the secretive nature of Closed Source Software utterly non-existent and it doesn't take a rocket scientist to see which is the better way to insure fewer bugs. Other dynamics, since Open Source is in many cases either voluntary, a labor of love, or a modification of some other program to better fit ones own needs, there is no time table, no deadline to meet, the release date, when it comes, arrives because the programmer is good and ready, to release it. Quite the opposite from the pressure cooker world of Closed Source software, where beating the competition to market is far more important than getting the last few bugs rung out.