Stack Overflow, as most developers will already know, is a question and answer site for programmers. It’s perfect for mainstream development questions in any programming language, and has also become the support site of choice for some newer programming communities such as Android developers. 
It can also be used as a barometer to see which current open source GIS projects have gained traction in the mainstream programming world. I took the full list of OSGeo projects from http://www.osgeo.org/ and ran queries on the site to see how many questions there were for each project. The results are as follows (as of May 2010):