If you plan on participating in the public beta of OS X Yosemite, you should use a secondary Mac. I’ve been using Yosemite since the first developer release and it is very stable, but it is still in development, which means things can go wrong. Putting beta operating system software on your production machine is never a good idea. You should also make a full backup of your machine.
Since Yosemite is still in development, not everything is going to work as it will in the finished release. Some services may not work as expected, and in fact, some features require iOS 8, which is not part of the public beta program. In other words, those features are not going to work at all.
I’ve been using the betas since beta 1, but for sure there are still many rough edges.
If you can’t tolerate the occasional crash or Hiccup, don’t install these beta’s. These are not the Google type of beta, it’s a real beta version where the software isn’t fully ready yet.
Next to this, I can say that the software is very nice (when it’s working) and is surely a step up over Mavericks. They’ve upped really the game with the iOS 8 integration as well.
My 2 favorite things from Yosemite until now:
The messaging integration with the iPhone and the new system fond: Helvetica.