The public beta
Although the OS X Beta Seed Program debuted back in April, Yosemite marks the first time a major new version of OS X has been available to the general public before it's actually released. As Apple puts it, anyone can "join the OS X Beta Program and help make the next release of OS X our best yet." Specifically, the public beta of OS X Yosemite is available to the first million people who sign up.
Apple is letting-nay, encouraging-end users to test beta versions of Yosemite.
For Apple, the Beta Seed Program will be a legitimate testing program that should produce far more data--bug reports, hardware configurations, and the like--than the company could ever generate from developers and employees alone. But it's also a boon for third-party developers. These developers will be able to test their own software, widely and publicly, on Yosemite before the OS is officially released, which should mean that many more Yosemite-optimized apps will be ready on Day One. (And, let's be honest, that's as good for Apple as it is for users.)
Of course, as Mac geeks, we're excited by the opportunity to get our hands on Yosemite several months early. But it's not something we recommend to everyone. Beta software is, by definition, not final-release quality, so there are bound to be bugs, some of them serious. If you're even considering signing up for the Beta Seed Program, you should have multiple good backups, and you should ideally do your testing on a Mac that isn't your main computer.
But if you have the resources to do these things; you're somewhat tech savvy; you're willing to put in the time to report bugs that you come across; and--perhaps most important--you understand what beta means (and won't blame Apple or third-party developers for any problems you might have, or data you might lose), then, by all means, sign up.
Bonus: The new (old) Dock
This isn't a big one, but it's a welcome one: One of the little things a number of Macworld editors miss from Mountain Lion and earlier versions of OS X was the two-dimensional, translucent Dock. Apple did away with this elegant, easy-to-view Dock way back in Mac OS X 10.5, but with a quick Terminal tweak (or the use of a third-party tweaking utility), you could still opt for it up until OS X 10.8. But in OS X 10.9 Mavericks, Apple removed even that hidden option--you were stuck with the (in my opinion) ugly, cluttered, 3-D appearance. With Yosemite's new interface, the flat, translucent dock is back. And I love it.
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