It's just never occurred to me to do so - the only time I ever know I have hot plates is when being served in a pub and something's been microwaved on it. I usually bring the mains and sides to the table for people to self-serve from (not wanting to give people too large/small portions) and it's just not really something I do, or have noticed others doing when having dinner at theirs apart from a v posh cousin who no longer works and has a massive triple oven in her house in Islington and therefore wrote it off as some odd posh phenomenon