I use metric units for actual scientific calculations, but I've honestly still never gotten an intuitive feel for them. If someone says it's 10°C, I still have to put in some small but extra mental exercise in to think "ok, so that would be a little above freezing then..." but it would take me a bit of time to pin it down to 40s or 50s in °F. But if given that same temp as it's equivalent 50°F, I'll have an understanding of what to expect in under a second. It's even worse for me with speeds: I can work with m/s on paper but if I really want to get a feel for it, I've got to have my mph.
That's really the big hurdle to it's adoption in the US, compounded by the fact that our average citizen is very stubborn and resistant to such change. Or the "wasted" costs to develop both new and transitional signage for things like speed limits or grocery weights.
I'll give you the stone, but for liquid volume Americans can't hate much there... our cans and small bottles are in fl oz but we also have 2 litre bottles... and then there's the little difference like American pint vs. Imperial pint...