OS X: Is there an open source screen recorder?
You've answered your own question, but I thought I would flesh it out a bit.  

You are correct that QuickTime will record a window, or the whole screen, but it only does so with the version of QT that ships with Lion. It wasn't available in earlier versions of QT or OS X (I'm not sure if the latest QT would do this on an older OS - I don't have one to try it on.)

I was pleasantly surprised to see that it now had that functionality - there really aren't any other free or low cost options.