I'm not sure how you guys manage with this being your main OS. I've been using it for a while and it pretty much frustrates me daily.
1) My fan is ALWAYS on. Know only a few of us experience this but it's pretty bad
2) Tablet mode has so many bugs and is pretty inefficient right now
3) At times, the computer just doesn't wake up from sleep. Just stays at black screen. Happens almost daily
4) At times, apps open up in desktop mode almost as though it's opening on a smartphone (so much smaller screen estate). Some only have the title bar and have to be dragged to see the full app
5) Battery life is absolutely horrible. It appears the Surface Pro 3 never goes to sleep so if put in a bag, just keeps bleeding battery until it runs out. That only takes about 3-4 hours for me when not using it and it's in a bag partly because it becomes hot (which I suspect is why the fan is always running)
6) Does anyone else have to use win+power button to unlock their screens at times? I'm not sure what prompts that but when it happens, it's an indicator that the SP3 is about misbehaving
7) At times, the start button stops working and I'm stuck in an opened app. It's impossible to switch apps (alt+tab or win+tab doesn't work) and can't get to the start menu or start screen. Only solution I've found is to restart and this happens about every 2 days
8) A lot of apps that worked in Windows 8.1 don't work for some reason. Tapatalk can't get past the home screen, Surface Hub no longer works. My Craigslist app doesn't work. then, some new Windows 10 replacement apps still don't work e.g. People.
9) The Mail app is pretty horrid right now. Can't deal w/ attachments and never downloads mails completely. I have to select download the full mail and it takes a while before that gets done
10) The Photo app doesn't use the local library but instead, tries to stream from OneDrive. Makes no sense as I have all my pictures synced from OneDrive locally but it still tries to go online. It seems like a huge regression so far.
11) Spartan becomes extremely slow after about 7 or more tabs are opened. I've gone back to using IE
12) For some weird reason, the internet seems much slower in Windows 10 than in Windows 8.1. Speed tests show same results but pages take longer to load. Must be some optimization not working out well
13) MS said a fix was coming a while back but still can't download music using the Music Preview or regular Music app
14) Store Beta has now way of showing recently updated apps so I can at least look forward to some apps being fixed
15) At times, pen stops working for no apparent reason.
That's all I can remember for now but I'm sure there are more. Even right now, typing in IE, the text's showing up much after I've typed and this is after a recent restart of my PC with nothing much running.
I did do a clean install.
Tbh, not sure how others have such good luck with this build. I use it as my daily driver but with a lot of frustrations. I've tried to revert to Windows 8.1 but that's looking like a lot of work cos I've lost my previous installation. Looking forward to the next build soon though., If that still has many issues, I'll figure out a way to revert.
It's rather refreshing/depressing to have become a geek again for the first time in a decade and all over nothing more than windows updates 
