9. You won't be able to try out Handoff or other Continuity features
Several key Continuity features aren't included. Apple lists phone calls, SMS, Handoff, Instant Hotspot and iCloud Drive as features that aren't fully baked enough to be included in the beta. Several of those require iOS 8, which Apple is not making available in a prerelease state to beta testers (though members of Apple's iOS developer program do have access to preview releases of iOS 8).
10. The beta agreement has confidentiality clauses
Apple is perhaps becoming more open under CEO Tim Cook, but the company still requires some confidentiality regarding unreleased products. The beta-test agreement for Yosemite defines the beta as "Apple confidential information." This means that you are agreeing not to discuss or demonstrate -- in person or online -- your use of the beta, unless you're talking to other beta testers. You can, however, discuss any information that Apple has already made public about Yosemite, since Apple no longer considers information that it has previously disclosed as confidential.
11. Using a Mac that meets the minimum requirements may not mean great performance
Yosemite is designed to run on a range of new and older Macs (the requirements are essentially the same as those for Mavericks and Mountain Lion). The oldest Macs that can run Yosemite include iMacs and MacBook Pros released as far back as 2007. Required specs on supported Macs are 2GB of RAM and 8GB of free storage. This means that you can technically install Yosemite on several older and low-powered Macs.
Your experience, however, is likely to be poor and performance notably slower if you use a Mac that just barely meets the requirements. Although it's difficult to gauge at this point what would be ideal, 4GB is probably the lowest amount of RAM that would enable decent performance (as it is with a Mac running Mavericks). As with most things in computing, the more memory you have, the better.
It's also worth remembering that, as with Mavericks, not all supported Macs have access to all features. AirPlay Mirroring and AirDrop, for example, aren't supported by some older Macs. It's also likely that some of the Continuity features like Handoff in Yosemite won't work on older Macs that lack support for Bluetooth 4/LE.
12. You can revert back to Mavericks if you choose
If you decide that you're not enjoying the process of beta-testing Yosemite, you can revert back to Mavericks. If you've installed Yosemite on an alternate drive, the process is simple -- just reboot from your primary startup drive. If you've installed on your primary drive, you're likely to need to wipe the drive and install Mavericks from scratch or from a backup (another reason to ensure you perform a full backup before installing the Yosemite beta).
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