My biggest problem with metric v imperial is that in the UK we still seem to use a mixture of both.
The UK use metric measurements for buying/selling stuff but our roads etc are still in miles. We buy petrol by the litre but then quote our fuel consumption in miles to the gallon. Most people can quote their height in feet and inches and their weights in pounds without having a clue of what they are in cms or kgs.
I learned 'metric' at school but since at that point much of the 'real UK world' was still selling stuff in imperial measures etc (until a few years ago), when I started shopping for myself, I had to relearn everything. I still have recipes in one or other and measuring cups in the wrong things.