That said, one of Apple's great talents is creating designs that, while being a little jarring on first glance, make the previous design look outdated. Fortunately there are plenty of examples of Yosemite's interface in the form of screenshots floating around the web. Explore them and consider just how averse you are to change. My guess is that you'll adapt fairly quickly.
And then there's the "ready for primetime" consideration. As operating systems become more complicated and rely on pieces outside the confines of the computer (meaning, in this case, iOS and iCloud) it seems that version 1.0 releases are not nearly as stable as the version they're replacing. Much as we wish it were different, we should accept that there will be problems with a brand-new Apple operating system. (And Windows operating system. And Android operating system.) Yosemite will be no exception.
I've long been a proponent for creating a setup so that you can dual-boot your Mac. On one partition or hard drive maintain the operating system you currently have along with all its apps and documents. On another, install the new OS and start living with it. When you encounter problems (as you likely will), gauge their severity. Are they mere annoyances? Perhaps you can put up with them until a fix is issued. Do they prevent you from getting your work or play done? Your best strategy may be booting back into Old Reliable and waiting for the inevitable update that adds the improvements you're looking for.
The bottom line
So is it worth your while to dive into Yosemite now or not? The ideal candidate for this update is someone who embraces Apple's vision of the future. You own modern Apple devices and see the advantage of easily passing data between them. You're unafraid of storing and syncing data in the cloud (you even appreciate its convenience). You like the idea of your Mac being able to pull in information from the Internet and present it within its search utility. And you're willing to give a new interface design a chance.
If, on the other hand, you prefer doing things as you did in the past--sync your data locally, have less interaction between your Mac and iOS devices, work with an interface you've grown to love over the better part of a decade, and go to sleep knowing that your Mac is going to behave tomorrow just as it did today and six months ago--there's no shame in leaving your Mac exactly as it is.
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