I know about the open source philosophy and about some websites which are hosting open source projects: sourceforge, github, codeplex.
The thing is that I'll like to learn form some open source projects, but because I'm a beginner I'll like to see how a certain library is used. For example I'll like to see how PHPExcel, ImageWorkshop, TCPDF, etc ... are used real work environments. Sample codes which come each library are useful, but I'll like to see how code works in real projects.
Basically my question is about how to find an open source project which use a certain library?
I not sure this exactly what your asking, but a Search :google: for "github PHPExcel" brings up a lot of results.