I may not be the best person to ask, because I am a compulsive "early adopter" of nearly anything to do with computers and software, so you need to take that into consideration when reading this post.

Given many — perhaps most — applications will have to be updated for full Yosemite compatibility and applications such as iTunes, iPhoto and no few others will have a new library structure and there are even changes in HFS+ (Mac OS Extended) volume structure, the only safe way to fully revert requires a complete wipe (repartitioning) of the boot drive. Rather than relying on Time Machine, I would instead clone the 10.6.8 volume to another HD using Carbon Copy Cloner or SuperDuper. Of course that will cost you any data changes that you make while running Yosemite, and if you use iCloud in Yosemite very little or none of that data will be available to your in 10.6.8.

Having said that, I have been running Yosemite since early in the public beta and I am quite happy with it. From personal experience and as an observer on these forums and the Apple Discussions the vast bulk of the problems I have seen reported are the result of out of date software, drivers, etc. There is very little software that will not need to be upgraded or updated for full Yosemite compatibility and incompatible or semi-compatible software will cause all sorts of problems. That will only become more acute as OS X continues to develop and OS X 10.11 is already in the works and OS X 10.6 has already dropped off of Apple's support window.


If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein