iWeb & Mountain Lion OS X 10.8
I installed Mountain Lion and iWeb seems to work fine although I still find it more convenient to launch and use it in Snow Leopard from an external drive.
Downloading and installing takes a fair amount of time and I did make sure my bootable backup actually worked before attempting it!
The only reason I upgraded was to run the latest version of Xcode. Otherwise I think Snow Leopard is a far better OS for desktops.
My biggest problem is getting used to my mouse scroll wheel working backwards and I was relieved that I could get away from the new look in Mail by selecting the classic layout.