I don't know if there's any universal etiquette, but personally I find it highly annoying when people abuse notification levels. Most room-like chat systems have a way to notify everyone in the room, like @here. IMO, you should only use that if your message is both important and time-sensitive for every person in the room. Sorry, no, it's not important to everyone else that you can't figure out why something isn't working.

Even more annoying is the people who post a message with max notification and lots of words about how it's super-urgent, and then don't respond for half an hour when you ask for more details. I guess it's not really that urgent if you can't be bothered to pay attention to responses to your question.

Or people who post screenshots of long error codes that you'd want to look up. If you want me to spend my time to figure out your problem, please take 5 seconds to copy and paste the error code so I can search it in other systems easily.

I also find it annoying when you help someone with some random thing, and they now decide that you're now their universal go-to mentor and expect you to fix all problems with everything.

ESR's page on How To Ask Questions would be a good read for a lot of such people: http://www.catb.org/~esr/faqs/smart-questions.html