I reverse migrated from ML to Lion months ago because there seemed to be too many problems with too many applications and performance problems with ML. I started off with 10.8.2, then upgraded to 10.8.3, and although some bugs were fixed they weren't all fixed. ML seems to be picky about older hardware, which is what I've got (2009). In any case, when I reverse migrated, I backed the ML partition off onto a FireWire drive by cloning it via Disk Utility. This is a really, really old FireWire drive (2003, to be exact) and I'm surprised it's still working. In any case, I updated it to 10.8.4 just to see if things are fixed. I'm still using Lion, but I noticed that the FireWire drive was making some odd sounds. I took out my copy of Scannerz and tested the drive and the historical profile of the drive is WAAAAAAY off. The latter is supposed to be a sign of impending failure. This is a FireWire drive so I'm not getting SMART status on it. Just to be safe, and if worst came to worst I used Phoenix and made a Phoenix Boot Volume on a USB flash drive so I can re-install ML quickly if I need to. I'm using the ML partition now and it's still working...at least for now. I figure if worse comes to worse and the drive actually dies on me I can use the Phoenix Boot Volume to re-install the OS and then migrate everything from another partition. Here's what I've noticed that seems to be fixed with ML: Memory management seems better. Once in a while, particularly when Safari was using Flash it would go balistic. Sometimes Safari Web content would go ballistic as well. This now seems under control. Spotlight doesn't seem to wart-hogging it up all the time. This was probably my biggest complaint, and it seems a lot better. Using Activity Monitor it seems more efficient. Some of the older Apple Apps that I imported from a series of upgrades now appear to be working properly. They used to crash on exit, now they terminate normally...at least the few I've tested do. Notes now seems to be working. I don't like the idea that I need iCloud to transfer from it but I can tolerate it. Before it was crashing all the time. Now it looks like it's working properly. Erratic delays are gone or at least greatly improved. Previously, sometimes I could click on the dock to launch something and it would pop up instantly, other times it might take 10 seconds. This was REALLY annoying, especially if I wasn't running anything on the system. I liked ML, but couldn't tolerate the bugs and some of the performance problems. Now they look like they're fixed, but I want to make certain before committing. I can't stand Lion and was seriously thinking about reverse migrating back to Snow Leopard if ML wasn't working. I'd prefer moving forward, not backward. Like I said before, I liked ML, I just wasn't interested in putting up with its faults. Any thoughts or opinions from anyone out there? In particular, can you think of any quick tests I should run on the system to verify how well it's working. I need to get it off that hard drive, which I'm sure is on it's last legs. I know ML works great on systems but not others. Opinions?