As I wrote a few weeks ago, I went back to the Yosemite Beta (or, more specifically) the Developer Preview. Apple released Gold Master Candidate 2 last Tuesday, followed up almost immediately with Candidate 3 two days later.
While the MacRumors 10.10 Forum remains abuzz with complaints about things that still aren't working properly, it seems from my very unscientific and non-professional viewpoint that most of them are of the "if you stand on your head and shake your right foot vigorously, your left hand starts turning purple" variety. Maybe I have a very generic setup and use very generic applications, but I haven't experienced any of the issues that people are recording. In the interest of full disclosure, there are still a few minor graphic inconsistencies, and I still haven't fully solved the Magic Mouse disconnection problem, but with Apple's next big event coming up on Thursday and its expected release of Yosemite to the public at that time, I would say it's damn close to being ready for Prime Time.
Others, of course, may disagree.
Has Apple EVER manufactured a mouse that was worth 2 cents? The round puck and single button mouse were the WORST mice ever made. Totally useless. Go back to your Dell BT mouse, it's much better.