I want to once again reinforce the idea that the optional sideboard rule isn't something you can beat other players over the head with. You can't just show up with a sideboard and a Wish suite and declare you're allowed to play it. It's an optional rule, not a part of dogma. If you want to play with the optional rule, then get the agreement of your group beforehand, please.
Understood and strongly agreed with. Sideboards are a decision that should be made by the group, not by one player who wants to modify their deck between games.
My question was, are there actually groups that use sideboards? If I were to add sideboards to all of my decks when I visit new games stores and tournaments, could I ever expect to actually use them?
Based on my experience, no one uses sideboards and they should probably be removed from the listed rules (even if they are optional). But I'm curious to see if other people's experiences match up - it's certainly possible that sideboarding in EDH is more popular than I give it credit for.