After installing Mint14 MATE with Compiz, I ran into a nasty Issue with theming window borders.
After some fiddling around, I found the solution to this.
Even though Compiz is assigned as window manager ( don't forget to activate teh CCSM setting 'Decoration', or you'll end up with no window decorators at all) , the Gnome Tweak Tool is required to apply themes to the window borders, as Compiz uses the GTK Window decorator.
Now, when you want to use a different theme for your decorations, just installl the Gnome-Tweak-Tool, start it ( by typing gnome-tweak-tool in a terminal window), move to 'Themes' and change your window borders/decorations there by changing the 'Current Theme'.
Hope this helps some people around that annoying issue I ran into too.
If someone needs additional info, just contact me.