I upgraded 14.04 to 16.04. There was a glitch that was widely reported as borking the upgrade; I just did a hard reset, booted back to Ubuntu and got a dconf window, Carried on and everything went perfectly. Apart from this it was the smoothest upgrade I've had in years - I normally always re-install but this time I don't think I'll bother. It's now working perfectly as my workhorse. Couldn't be happier.