i'm annoyed by this behavior, too. since upgrading to ML, i'm giving safari a chance (always have used FF). i have generally liked safari, so far. however, reloading is annoying for me, not because of slowness, rather it is only when prior data is lost due to the reload.
as a side note, i STILL don't like the way safari handles tabs!!!
This issue has caused me to move to Firefox/Chrome for a bit. Looking for images on Google a couple times a day and having all the images reload each time you go back from checking out a picture is enough to drive anyone batty.