I installed KDE4 on my desktop today so I could finally try out KWin in all its glory. If you haven't tried it yet I highly recommend it. KDE4 with desktop effects enabled is simply gorgeous. It's fast, responsive, and comes with a nice array of effects options.

Dim Inactive is one of the first effects that I enabled and I really like it so far. One of my pet peeves with Oxygen is that it doesn't change the color of a window's title bar to show which is active, but with Dim Inactive enabled this no longer matters. Instead of changing the title bar the windows in the background are darkened to create a clear contrast that makes it easier to focus on the foreground window.