I just finished installing El Capitan over my Snow Leopard which, other than exorbitant time (Took well over an house to install) and not seems to be up and running, still have to load certain updated apps and buku data files.
My problem is that when I return to 10.8, I can no longer bring up my applications which should not have been affected by the install of El Capitan as they are on a totally different Hard Drive. In particular, I was trying to bring up a file contained on an old Zip disk (250mb) that until yesterday came up clean. after attempting it several time, I tried to open Pages and though it is marked as open, nothing whatsoever shows on the screen. I have not checked this with the other apps but suspect they will be similar if not identical.
Sparkgapper