My tipping point was not being able to figure out how to shut down the computer in Windows 8 (not 8.1). I've used Alt+F4 to shut it down for months because I legit couldn't figure out that the shut down button is in Charms.

They've moved it back to start in 8.1, but by that point I've already switched to elementary OS (beta of 0.2 Luna), and that's (mostly) where I've stayed for the past 10 years (there were a couple of attempts of switching to GNOME, they've all failed).