This year, the end of my recreational riding season will probably coincide with the end of 'commuting with a HRM' season, also known as 'commuting in a bike jersey, not a jersey over a t-shirt' season. I can wear my HRM even under a t-shirt but it's more of a pain, so mostly I don't.
I'd try to compare my commuting heart rate at the start and the end of the season, but there are so many confounding factors.
(That I wear a HRM during commutes at all is due to @gnomon )