I forgot to mention that I already have SL. It is STILL on my old MacBook and am currently using a late 2010 Air AND with the iPhone 5s with iCloud, well, I thought I'll NEVER upgrade to ML. Now I'll have eat my own words.......
SL is amazing. I never had any problem with it and you are right about Apple keeping it for older systems, upgrading to ML, etc. With Safari 5.1.10 on SL, I noticed that I was having problems with three websites - viewing them. I opened Firefox and all three worked perfectly. I had the similar problem when I had Panter on my lovely eMac.