When I saw the title of this thread I avoided reading it because I was sure some poor soul was being lambasted for asking if it was ok to wear a dive watch in the shower. What a relief to see the question was much more broad than just the shower, and everyone (almost) is playing nice.
Since you asked, I bought a Submariner a decade ago to wear in the water. The old Speedmasters or other vintage watches were not going to be exposed to more than drizzle. The Sub was great for swimming, cycling, etc. and since it often became very sweaty, I would shower with it mostly to clean it up. I can live with soap scum, although I never noticed that being an issue. It was nice to get it and the NATO squeaky clean after a good sweat. Since, I've pickup up the MKII Nassau and the Watchco SM 300,(the sm300 master coax gets babied to avoid scratches) and both are used for swimming and water days, and both go in the shower to get clean along with me. Yes, I could have bought a cheaper dive watch, but cmon, none of us needs these watches when modern quartz watches would make much more sense. We like the look, and we like that we can afford to waste money on frivolous things, and many of us want others to know, too. I highly recommend showering your Sub or SM now and then. They all get dirty.