There was an issue with the 3rd developer preview that caused Accordance to crash when opening the library window (Nathan Parker reported on it here--although I might suggest his use of major was a bit of hyperbole ).
That issue went away for me in the 4th preview, which I believe is what is being released in the beta program today. I haven't had some of the other random crashes in Accordance that Nathan described in the above-linked thread.
I've had trouble with folder icons disappearing, but a reinstall today fixed that.
A handful of programs have not worked on and off with the previews.
I would definitely say not to install the beta if you only have one Mac. I'm down to one Mac and I installed anyway, only to regret it afterwards. Each build has naturally seen improvement, but I've been part of Apple's appleseed program for a number of years, and Yosemite was initially the buggiest OS X beta I've used. I think that's because Yosemite is a very significant update compared to some of the recent updates.
If you only have one Mac, I would suggest proceeding with great caution.