If you don't have the time or dedication to provide that kind of feedback, you're probably better off just waiting for the official release this fall. Apple would surely rather give a beta-program slot to someone who will be a good tester--and, frankly, we agree, as good beta testing means a better, more-stable release of Yosemite for all of us.
Of course, you shouldn't expect Apple to change major features based on your feedback alone, and general griping--for example, venting about how you don't like the "flat" look the company is adopting with its user interfaces--is likely to fall on deaf ears. But bug reports are vital feedback that can, and often do, result in fixes and improvements. And if the company receives enough constructive feedback about a particular feature or interface, there's a good chance Apple's engineers will take a look--if not for the initial release of Yosemite, perhaps for a subsequent update.
How do I send that feedback to Apple?
The beta version of Yosemite includes the Feedback Assistant app. You just launch the app and follow the steps. For example, on the Questions screen, you choose the general area about which you're providing feedback (for example, System Crashes, AirDrop, or iCloud Keychain); and then any specific sub-area, if applicable. You describe the issue in a single sentence, and then provide a detailed description, including any specific steps that reproduce the issue.
The Feedback Assistant will request permission to collect diagnostic information from your Mac, and give you the opportunity to attach other files, such as screenshots that show the issue you're reporting. Finally, you'll see a summary of your submission; click Submit to send it to Apple.
How do I know if something is a bug or not?
In general, if something doesn't work as it should, that's a bug. If you can't figure out how to do something, that may be a bug, or it could just be an interface that needs tweaking. If something works the way Apple designed it to work, but you just don't like it, that's not a bug, but your opinion may still be useful feedback.
The good news is that you don't have to worry about which is which. Just use the Feedback Assistant app to provide your feedback. Apple will sort it out for you.
What if I'm having trouble with a third-party app under the Yosemite beta? Do I report that to Apple?
Yes. In fact, the Feedback Assistant app even provides a 3rd-party Application Compatibility category when submitting feedback.
However, in most cases, you should also take a few minutes to provide that feedback directly to the app's developer, as Apple is unlikely to forward it. Most third-party apps provide a button or link (in the Help menu, in a preferences or settings window, or somewhere in the app's main interface) for contacting the developer. If you can't find one there, check the developer's website, or, for apps purchased through the Mac App Store, use the Support link on the app's Mac App Store page.
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