I've just tried the Qt4 backend and noticed that, different from the previous backend I was using, the last command of a script pylab.show() does not raise the figures to the front (they show up but in the background). This is the case at least on my OS X machine. I personally feels like the figures taking becoming the active windows should be the right behavior. In case, this is valuable to the project, please find below at patch that achieves that behavior.
raiseFocus.diff (451 Bytes)