I joined the Beta program for OS X Yosemite. I feel pretty comfortable installing Apple beta releases. Never really had any serious problems with them before. Can't wait to see what the new features are like.
Has Apple included the new "Photos" app in the beta? I've been using iPhoto for 7 years now, and I'd rather not have to use an iOS-like photo organization tool on my Mac. Otherwise, Yosemite seems like a very exciting upgrade. What Mac are you using? It looks like my 2009 Mac Mini will run it, but considering how quickly Apple is dropping support for older products, I'm afraid I may have upgrade in the near future.
I shouldn't be able to run OS X Mavericks on my 2006 Mac Pro. Where there's a will there's a way. left monitor is OS X Mavericks, right monitor is Windows 8.1 Update in a VM. Mac Pro has dual quad core Xeon processors and 24 GB of RAM. Windows VM is configured to use two processor cores and 8 GB of RAM. Not too shabby for an 8 year old machine.
I checked, and iPhoto is still on my MacBook after upgrading to Yosemite, and it still works. The new photo app won't be released until early next year, and they will halt updates to both iPhoto and Aperture.