I have an older MacBook pro, but I've been running SL on Macs since I started in 2007 with absolutely no problems at all until I tried upgrading to Yosemite in November shortly after it was released - I'd previously upgraded to Mavericks and had no problems at all. But I had all kinds of problems with SL, and it didn't matter which viewer I tried (Linden, FS or Singularity) they would crash and freeze constantly. Within three days I couldn't even log in to Yosemite, it would freeze during the login process. I managed to get it repaired and rolled back to Mavericks since when it's been running SL and all my other apps absolutely fine. Apple have not been able to explain what went wrong, the only theory they had was that there were problems with the graphics drivers, but since it's been fine with Mavericks, I haven't tried to upgrade again, even though my short experience of Yosemite for all other Mac stuff was really good.