I got a spot in the Apple OS X Yosemite public beta! It was limited to the first 1 million public signups.
Just installed it and so far so good. During the installing process though, my iMac 27" (early 2014) kicked up the fan full blast and blew out all the dust! Thought it was smoke for a second. Phew!
Definitely digging the new look. Finally feels like the OS X has arrived in the digital (flat) age. Will definitely try to do a short write up after a bit more use. There MIGHT be a few spots left in the beta program if you're lucky so hit up the link if you're keen:
It would definitely be wise to install it on a secondary machine and not your primary work horse. You can also try and install it on a partition or external drive.
I have it installed on my main computer, although I have created a Time Machine backup pre Yosemite. If it crashes and you don't hear from me for a while, you'll know why haha..