Connected standby
Microsoft, get rid of that half-baked junk you conceived with Intel.
Connected Standby is by far THE most annoying feature of Windows 8.1 on a tablet - you can't turn screen off without tablet going to sleep, you can't leave any applications that need network access running in background (unless they are Metro Apps, and there are not many useful amongst them), it drains battery without any particular reason for it, and you just can't disable or work around it.
Microsoft, fix it and I'll buy another Windows tablet (and I really-really liked proper operating system on a tablet for about 4 hours, until discovered all issues above).