Part of the charm of this game is the pomp and circumstance of a face to face game. Manners play an important part of that. I agree with Phelan, in that your opponent can make mistakes that may change the outcome. However, you really have to be paying attention to the positions if you do resign. Stalemate is another import point. I've seen players losing a game throw themselves into a draw to save points.
What is chess etiquette?

LoL at rule #3 :D
and don't delay. Like when people lose, they'd love to use all of their time before making a moves, worse, they use their 30 days vacation:D
they try their best to delay our win.
oh well, those are not against the rule anyway.
and say Good Game after a game is finish
I use to rated somewhere in the 1350 on live chess and whenever I beat a 1400+ player, he or she stomp away without a word. He or she doesn't even answer my GG. =]
that's just my oppinion.

That is certainly true - as the reactions to this discussion (http://www.chess.com/forum/view/community/7-deadly-sins) indicated.
What some people find particularly upsetting is when their expectations are disappointed. One approach that may reduce this potential frustration is to be explicit, up-front about your own behaviour. If you are the resigning sort, say so. If you are not, say so. Same for chatting, using reference material, moving slowly/quickly, timing out, etc.
As Billium248 suggested, group membership is one clear indicator. Other indicators include Extended Personal Profile (http://www.chess.com/forum/view/community/who-is-player-x) and Essential Chess Type (http://www.chess.com/forum/view/community/its-another-rollover).

I'm offended by opponents. Their interests are contrary to my own. Chess etiquette dictates that they should checkmate themselves immediately after the game begins.

One that really rubs me the wrong way in Live is players who just close the window instead of resigning. Or alternatively closing the window as soon as a game has been lost without enough time for me to type "Good game" -- even if you're not polite enough to type it back, at least let me say it.

I am up front and polite with everyone I play and seldom have any problems. I think everyone here has made valid points about resignation!

I used to wonder about saving face by resigning a losing game, and that may make sense for players at a high-enough level where they can see the game to it's end in their heads without playing it out... Unfortunately, I am no where near that level.
At some point in a game, I may feel that I'm pretty sure I'm going to either win or lose, but my motivations for playing is not necessarily the end result, but rather the experience and practice. I'm starting to feel that I won't be able to get good at end-games if I don't play games to the bitter end. And who knows, someone could make an error and the entire game could change, or a stalemate trap may work...
I had a game where I was pretty sure I would be mated in 2 moves and there was nothing I could do to avoid it, but my opponent didn't see it and I ended up winning in the end. I've had some games where I missed the forced mate (the computer analysis politely informed me so after the game) because I was concentrating on position and material gain, rather than looking for the mate.
So my preference now is to finish games to the end. I suppose if I really felt I had no hope of winning I could offer to resign and give my opponent the opportuninty to decide if they'd rather play it out.

I used to wonder about saving face by resigning a losing game, and that may make sense for players at a high-enough level where they can see the game to it's end in their heads without playing it out... Unfortunately, I am no where near that level.
I think this is really a mis-conception about high ranked players. As if we can see the game to its end without playing it out. Rather I believe higher ranked players see the truth of the position (not the variations of that truth).
Seeing the truth that a position is lost is quite different than playing 12 or 15 moves ahead with sub-variations. ( I think only a handfull of GM's in the history of chess could do this.)
I am of the opinion that after book move openings it is the player who sees the truth of the position who usually wins. Truth = Understanding the threats and the potential in the given position.

Agreed -- it's not an exercise in brute force calculation, it's an understanding of the dynamics of the position as a whole and how they are likley to play out, generally speaking, with good play from both sides.

Ettiquite is a little bit different for different types of chess.
Correspondence chess -
... Resign once a lost position has been achieved.
... Do not question vacation or move speed.
... Offer only 1 draw in the course of a game.
Blitz Chess -
... Accept reasonable draw offers
... Acknowledge greetings
OTB (Over The Board) Chess -
... Pregame handshake
... No more than 1 draw offer
... No whispering to your opponent (go find a tournament director if you have an issue with your opponents play).
... Postgame handshake
... Reset the pieces at the end of the game.

Ettiquite is a little bit different for different types of chess.
Correspondence chess -
... Resign once a lost position has been achieved.
... Do not question vacation or move speed.
... Offer only 1 draw in the course of a game.
Blitz Chess -
... Accept reasonable draw offers
... Acknowledge greetings
OTB (Over The Board) Chess -
... Pregame handshake
... No more than 1 draw offer
... No whispering to your opponent (go find a tournament director if you have an issue with your opponents play).
... Postgame handshake
... Reset the pieces at the end of the game.
My NEMISIS!! Calls me names when we play.

Hi immortalgamer,
I don't have any problem with trash talking amongst friends as long as everyone is OK with it. Otherwise you risk a visit from the ettiquete police...
Hi ih8sens,
I agree, though I find that people tend to be much more polite in OTB chess than on the internet.
=wild=

There are many rude people on this site. They are happy to play when things are going well but when they know that they are losing, they drag the game out as much as they can. If it's a 24 hour game, they will take 23 and a half hours to make a move. They know that they are beaten but instead of resigning, or at least play on with the person online, they spit the dummy by dragging it out. This to me is bad sportsmanship. Chesterton is the worsy for this.
THIS IF I LOSE