PortaWiki is going pretty well. We’ve got a couple of contribututors at the moment and getting good little bits on the various oddities of various platforms. I encourage you to check it out and add things that you know.
It’d be great to have a MySQL section there too. In versions previous to 5.0 for example, you may get different results from some math operations on different platforms as we used the floating point stuff. In 5.0 we have precision math so this isn’t a problem – but it probably caused somebody to raise an eyebrow in the past. Volunteers?