This post is an update to Make Gimp.app usable on a mac:
The “Click through” property on both Apples X11 and the X11 provided by XQuartz is not set. This leads to the fact, that you have to click on each X11 window twice: First activating it, 2nd pushing a button or whatever else. I hate this, i really do.
With Apples X11, open a terminal and enter:
defaults write com.apple.X11 wm_click_through -bool true
With XQuartz X11 enter:
defaults write org.x.X11 wm_click_through -bool true
This will help you with all X11 apps, like Gimp, Inkscape, Open Office and the likes.