You still occasionally see people talk about their weight in stone, but many just use kilos now, anecdotally.

In my experience, if you're looking to lose a bit of flab for the summer, you'd say you want to lose six pound to half a stone (which is 7lb) or whatever, but if you go the gym regularly and keep an extremely keen eye on your weight, or if you like to think you do, you use kilos. As a rule, you'd use imperial for eyeballing or for measuring things with a bit of play, but you'd use metric if you need precision.