Updated to PB4 (cGM) from Mavericks and it's been absolutely solid for me. I was expecting it to be unrefined and not efficient (like Mavericks GM was) but it's be great. Installed it on a work computer (I like to take chances?

) and everything has been working fine. I've read a few comments on the forum about memory but for some reason, memory is a lot better in Yosemite than it was in Mavericks, the obvious one being with Safari. In Mavericks, each tab you open in Safari had it's own process and took up a lot of RAM but doing the same thing in Yosemite, it's using a lot less memory.
Right now I have 5 Safari tabs open, Outlook, Excel and accounting software and I'm sitting at 6.92GB of free RAM. Doing the same thing in Mavericks I would be at about 4GB of free RAM.