I was writing that comment, and kept thinking of the possible annoying implementations. For example, I probably don't want a notification every single time someone within 1 mile sends a message.
Some seemingly sane ideas off the top of my head, which I think would be useful and not too annoying:
* A timeout, where I get a notification if there is a new message, after a period where no messages were sent near me
* Notification if I send a message with no reply, close the app, and then someone replies
* Notification if there is a particularly active conversation around me
* No way to copy text from other people
* No way to create hyperlinks (which would be awesome)
* Emoticons seem to disappear
* New people are very confused by the badges
* I had a weird bug where it kept asking me to wait 5s before posting, I hadn't touched it in ~10 minutes. It had been cycling between "Need 1 more person to unlock this area" and being unlocked for some of that time too.
Seeing the usage pick-up has been fun! Looking forward to seeing how things progress.