Wow. I'm glad you're not in charge. Five years with little change made? Progress? Who needs that when we can just go with the same crap for long periods of time.
As for your timeline, I don't know what you consider basic things. I picked up ML on day one, and Mavericks as well. I even used Yosemite until I handed my Air over to my sister. It worked for me.
I'm sure the majority of people won't run into issues because that's what Beta testing ensures. However, it really seems to me that more people are having issues than normal. WiFi issues with every release, performance issues, etc. Sure, it's a new OS, bugs are to be expected. However, a new OS every year means more bugs for more time. The OS spends less time being mature.
I'm not saying that a 5 year old OS is great, but sometimes a more mature product that lacks features but is robust and has almost no bugs is better than a modern OS that is full of bugs and instability issues, and by the time they do get fixed a new OS comes out with the same damn bugs again.
For example: In Lion and Mountain Lion, Photoshop had this bug that caused mouse clicks to get stuck. This was caused by some mouse event handler in OS X. In Mavericks, this issue was fixed, at last. In Yosemite, it's back again. Same thing with gestures not always working, scrolling not always working, and a bunch of small things that piss me off but many people won't even notice.
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You shouldn’t be early-adopting, it’s as simple as that.
But OS X is now releasing a new version every year. What counts are "early adopting"? It's now mid December, Yosemite was released 2 months ago, that's almost 20% of the release cycle. Should we wait for the OS to be halfway into its lifecycle to upgrade? Or should we wait for OS X 10.11 to be out to even upgrade to 10.10? It no longer makes any sense. OS X is now never in a state of matureness, it's always buggy and never fixed because by the time it's fixed a new immature and buggy OS is released that does pretty much nothing new other than be buggy as hell. Mavericks was basically the undoing of the crap that Lion and Mountain Lion brought in, so we could have just stayed with Snow Leopard until then.
A new feature in Mavericks was that Calendar was once again almost exactly like in Snow Leopard and everyone clapped and cheered.
People complained about Lion being horrible in terms of design and behaviour, and it took Apple 2 years to fix those. People did not complain about Snow Leopard. Wouldn't it have been easier to just not release Lion and Mountain Lion, let Snow Leopard hang around for 3 years and then release Mavericks? Then no one would have complained about how crap Lion and ML were.