Open source is a great idea. Find a widget that does what you want, make a contribution to the authors, drop it into your web-site and go forth. There are some great widgets and systems out there. Without Apache, mySQL, and hundreds of other packages the internet and systems development would be a more sterile environment.
But there are also all the other open source developments. Great ideas with some great programming, but could have done with a once over with someone who is experienced in the areas that the initiator is not expert in. On the one hand at least I have a starting point, on the other hand it puts some butter on earning my daily bread.
I was trying to think of how to compose an organised thread on this topic when I saw this excellent representation 
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The number one reason people ask me to look at their open source web-site is that they are starting to generate traffic and the site just gets slower and slower. The reason? SELECT alist FROM tablea, tableb WHERE tablea.id = tableb.id;. Learn how to use joins properly and we can all get to do more interesting and productive work.
Thanks.
