Regarding my grow rooms, I pretty well always refer to things in F, and always have. I can convert in my head though, say for example if someone here posts a question in C. If I answer, I'll typically reply with the F figure, and put the C figure within parenthesis so that all future readers (including the OP) have both.
When I'm speaking about outside temperatures, I almost exclusively use C, unless I'm speaking to someone (family, friend etc) from the US, and I'll do the calculation in my head and use F as the measurement.
I was at a gas station at Lake Louise, AB a couple of years ago, and had family visiting from Dallas and SF. We were going camping up by Jasper. I was driving a US vehicle at the time, so the temp on the dash was in F. One of them asked "what's the temperature in Celsius?". Took a sec, and spit the answer out.
Then, another Canadian filling at the pump adjacent to me, asks "how many kilometres in a mile?". I laughed, told them, and explained that with family in both countries, it's mandatory to be able to do conversions and answer appropriately for the audience
