I am not upgrading to macOS Sierra or even downloading the Dev Copy from developer.apple.com (Registered Developer). I've got some serious holdups about several of the key features. Apparently, as of now, the 'Gatekeeper' controls will not let you run non-Apple signed 3rd party apps, at all. There is a new filesystem and I am worried, especially in these pre-beta stages it will have flaws and create problems. Thirdly, I am concerned about the privacy and security of Siri as the Siri feature records and saves each voice command as a voice recording on Apple servers, and saves every single one, for their use. That's not privacy. And it all has me a bit concerned. I am holding off on Sierra for now and sticking with El Capitan, which is running pretty rock solid on my side. If Apple promises it's stable and won't bork your system, and opens up Gatekeeper to allow 3rd party apps, I might consider it. But I will test it on a test machine first (MacBook Pro) and not my Desktop. I have upgraded to Developer Previews before, been severely disappointed, and found it a nearly impossible task to restore my older system. I'm not putting this on my main machine as Dev Preview 1. Bad Mistake made. The finals all turned out fine. Late beta stages they get much better.