I have a fresh install of Mint 7 KDE. I installed Compiz and turned off the KDE effects in the Desktop control panel. However Compiz doesn't start when I log in. I have to manually run it and then it's fine.
I installed Gloria KDE on my laptop as well and added Compiz there too, but it starts automatically there.
The only thing I can think of is my home directory. On my desktop (where I have the problem) I moved aside my original home directory and linked to the home directory of my Ubuntu install, on another drive. I copied the .kde directory from the original into my Ubuntu home directory, and it all seems to have worked, except for this small glitch.