Just a heads up if you are about to install the new OS X, beware with the boot problem some people are having. There have been a couple of possible solutions given by different people, so be careful and backup all the things.
Also I noticed that after installing Yosemite, it brought up an old issue which I’ve fixed before (introduced by Mavericks). The _kerneltask process consuming almost all CPU available.
If you haven’t been through this before, check this post for more info. It’s pretty easy to fix.