I will simply say this: I rely on this machine for my living. So much so that I have a spare slightly-more-vintage Mac around at all times as backup hardware. There is no possible way I would upgrade to a new OS if it didn't work with my software, as I'd be out of a job. When testing Yosemite in beta, I put it on a separate drive from Mavericks so I could both troubleshoot and be sure to have one productive OS X I could count on.
During the beta process, I ran across some what for me would be "showstopper" issues with some programs breaking under Yosemite (a fair number of FTP programs, AIM, iMovie [of all things!] and so on).
As of Beta 6, I moved over to Yosemite full time for all my daily tasks. I have been there since. Apart from some minor programs and menubar items that need to update for Dark Mode (I'm looking at you, Radium!), this release is IMHO as solid as Mavericks was in its first release (people have very short -- and decidedly selective -- memories about this). Room for improvement? Yes. Good enough for production-level, mission-critical work? For me, yes (and I use a fairly wide array of apps). Stable? You bet.
I'm not saying other people haven't had issues. I'm saying I haven't seen them on this machine with the programs mentioned that I also use. Why? Maybe I'm lucky, or maybe my habit of routine maintenance, regular backups and (this last one hasn't been done yet due to travel) a clean install of a major OS upgrade has made a difference in my "luck." I have no doubt that some of the reports I've seen are clearly legitimate bugs in Yosemite, but either I don't run those programs, don't run them that way, or the problem just isn't reproducible on this machine.