I use imperial for most carpentry work, as that's still the standard for lumber in Canada. It wouldn't be difficult to adjust the nominal sizes of lumber to metric, but it gets more difficult with sheet goods. A 4' wide sheet is nominally 120cm wide, but it is actually 121.9 cm, which is a difference of about 3/4". This doesn't matter if you are doing new construction, but if you are replacing imperial sheet goods, it may give you a problem in spacing. Are there any Brits around who could tell us if they've made this change in Britain? Or Oz or NZ?
I do use metric if I want to know how much to cut off the end of a stick to make it fit. That way I don't have to mess with 16ths and 8ths of an inch.