I've been poking around reddit and a few other places for it - from what I'm seeing, there are three camps and it seems pretty evenly divided (ANECDOTAL):
1) Worked fine, everything works like before but better
2) It broke everything, but when I rebooted hub <x, y, z> it all came back up and works just like before but better
3) It broke everything, rebooting all my hubs had no change, I had to remove every device and re-add it and now it works like before but better.
There does seem to be consensus on Apple choosing better connected hubs now, instead of just doing it randomly it seems. Things like picking a wifi HomePod as a hub instead of a hard-wired AppleTV doesn't seem to be happening. It's showing preference for hard-wired devices for hubs now - things like that. I've also seen reports that people who started using Home when it first launch have some kind of userID associated with their accounts that cause problems that more recently Apple Home'd folks do not experience. Oh, and there are people reporting issues with not being able to add users to their home, or having to remove users before being able to add them back (because their access no longer worked) :
: Personally I'm between homes at the moment, so when I have the patience to completely reset my entire Home setup I'll pull the trigger and hope it's not the worst for me :-/