I just thought I 'd pass this on in case another member runs into the same issue as me.
I've been fighting brake drag now for a couple of weeks. After reading lots of threads and trying the usual stuff (brake bleeding, caliper clean & rebuild, setting adjustment screw etc) it dawned on me that it may be related to the powder coat on my hubs.
I whipped off the rotor, to take a closer look. Sure enough, the mating surface on the hub had a nice thick layer of shiny coating; something I had barely paid attention to when I first built the bike a few months ago.
Anyway, to cut a long story short removing the PC from the hub flange fixed the problem. No brake drag and a nice free spinning front wheel
If you're interested I used several applications of Permatex Gasket Remover and the blade of a Stanley knife to get back to bare metal on the hub.