I lived through the conversion as a kid, really it wasn't hard, school work (all those conversions, all that manual long division,) went away and got easier. We had dual speed limits up for 4-5 years.
in practice when you switch to metric you switch to natural units - a pound is about half a kilo a pint about half a litre (american pints are smaller) - you don't buy a quart of milk you just buy a litre, you go to the butcher and you ask her to cut you half a kilo of meat, no one asks for 0.23kg, that's silly
In the transition you use some useful equivalences: 2 inches are ~ 5cm - 3 yards ~ 1m, 30miles=50km 50miles=80km 60miles=100km (speed limits are easy unless for some weird reason you've chosen to use numbers that end in 5 rather than 0) 2pints ~= 1l (in the US) 1pint=600mL(in the UK, but half a litre will do for lots of day to day stuff), 2lb ~ 1kg
"cups" are am interesting issue: cups in the UK and US are different by about 20% (because the pints are different) so recipes sometime don't work well between them today, the metric cup used by everyone else is an intermediate size, as a result european recipes tend to work slightly better in the UK and US
as far as fluid ozs are concerned they're just such a mess they're best avoided