Please see github_auth48_experiment for context.
My biggest surprise - it is not as useful at communicating issues and changes as I thought it would be. One author was unaware of progress, and the AD never received notifications even when he was @mentioned. I also thought I knew a thing or two about Git and GitHub, but creating a workflow for the rtcweb-wg repo took time.
My sneaking suspicion - even frequent GitHub users are bitten by bad assumptions about how it works.
Things I liked - Being able to refer to issues and PRs with hashtags and have GitHub build hyperlinks in comments and commit messages. Automatic closure of issues when a PR was accepted is satisfying. Tracking of open issues is easy.
Things that were meh - interacting with Git and GitHub is not quick. Like other uses of GitHub I've seen in the IETF, technical discussions erupt on individual issues (see #843, which predated the AUTH48 issues but wasn't addressed by the authors until almost all the AUTH48 issues had been closed), and participants are slow to take the issue to a broader audience/ML (see the start of the email discussion).
Things that I would change next go around - the RPC should control the repo, which would allow us to merge the changes and add the right people as contributors so that they can (maybe) receive notifications (it may be a horse-to-water problem).