David Baker Architects, where Caroline works, got Slack about a year ago. They went from no IMs, no email lists, no wiki, straight to chat, so they have to learn all the etiquette we tech folks have spent the last decade sorting out. Can we dis-invite someone from a public channel if we don't want them interfering in the discussion anymore? When is it OK to make a channel private? Do we keep the existence of private channels secret? How do we communicate that not every posted item is an invitation for comment/critique?

There's also the question of what you can and can't discuss. And the general rule in tech is that you can discuss anything, with two notable exceptions.

The first is "numbers": revenue, burn rates, metrics, growth, etc. This stuff is guarded, not least because companies can run afoul of securities laws (insider trading) if they aren't careful when things are disclosed. So that sort of information tends to be a bit guarded.

The second is personnel data: performance reviews, the details of hiring and firing, bonuses, salaries, etc; disclosing that can adversely affect the business, but it's also a matter of preserving an individual's right to privacy.

Almost anythign is fair game, from strategy to why the CEO is a bozo, just stay away from numbers and personnel stuff.