I had some trouble getting the sub-processes to die properly when the saver deactivated or when you changed option settings. I think it works, but be paranoid about that.
I finally ported the webcollage screen saver to OSX. This will be included with the next release of xscreensaver, but here's a zip of just the one. Let me know if it works...
Current Music: Machines of Loving Grace -- Casual Users ♬