KSM is a great idea, much of its abilities are available in Fedora 12. I tried it and I had higher expectations to be honest.
That is not to say that it is no good - its great but there is a bit of a cost analsysis that should be done before implementing it. You dont get something for nothing - and in this case ultimately your offloading the higher memory usage onto the CPU. Depending on your hypervisor setup this might not be such a bad thing of course.
In my somewhat narrow testing of it I found that:-
a) Even with the same O/S images running multiple times the memory I saved was about 5-10%.
b) It effectively used about 50% of one CPU running the feature.
I think that to really see a benefit to this you have to be running a huge hypervisor with a ton of memory and cpus and a lot of guests as there is a plateau which beforehand makes it quite inefficient to use the features seeing as (at least with my results) the payback is less than 10% anyway.