basically we're supposed to be fully metric, just like we're supposed to be european, but none of us want to be, so imperial hangs around by force of public opinion.
there was alot of trouble recently with it being made compulsary for fruit and veg weights and whatnot to be labled in metric cos of the eu charter, but poloticians never miss a chance to be popularist so it got chucked out. same with road signs, all in miles.
for anything that matters, nuts and bolts, tools, anything that needs to be exact, its all metric these days. anything else you can take your pick. pretty much the same in usa no?