To answer Gossip I will say yes if there is something in place for it. I think etiquette begins and ends with the consensus of those involved in the game. In this site there is already a standard that supersedes what a group might want to do so its more about if they do it or not since its already set for them.
The biggest thing for me will be participating when you should. You know everyone will be waiting on you so the most courteous thing to do is show up when you're supposed to and if you can't because something is coming up then let us know beforehand so the Dungeon Master isn't holding up the game waiting on your character's actions.
You don't have to be perfect but writing properly is a plus for me. If you are writing in character then attempt to get your character's words to match the same time period. For instance if you are in the middle ages don't talk like you're an 80s rock star - that's just poor quality role-playing.
It will be good if RPGers use their Introduction to Post their schedules, emergencies, deaths and so forth and not the game Threads. When this is not followed their private notice detracts and it turns an entire Thread to focus on their personal issues. Please don't do that, this is one of the things explicitly mentioned in the Role-playing Game Etiquette Post. A link to the Role-playing Game Etiquette guidelines is available on every page of every Role-playing Game.
I will like to add to above that it will also be nice if they post if they're not coming anytime soon or at all so we can move on and stop bringing their name up in a game.
This is my opinion for tabletop and play by post. I feel that everyone should have fun. Players should try to be team players and not try to dominate the game. People shouldn't make min/max characters if the rest of the group isn't. It is best to balance your character to the rest of the group so everyone feels like their character contributes.
Don't argue every rule. There is one in almost every group that wants to argue with the Dungeon Master. Occasional questioning is okay but please don't try to argue at every step.
The level of etiquette varies among participants. Some care about their role and others do not. Some are polite and apologetic while others are arrogant and weird. I think the real character everyone comes out in the way they play. If there is one thing that gets to me is waiting on someone that goes and comes from a game as they please and don't think to give any explanation. I tend to ignore those characters but it does surprise me when the Dungeon Master treats them like a prodigal son. *laugh*.