What is the broader acceptance of resignation?
I would say that resignation is perfectly acceptable as long as 

1) It was preceded by a good-faith effort to play optimally.

2) All parties who are affected by the resignation agree on its timeliness.

The only times I feel a resignation is discourteous is when it negatively impacts people who were depending on your continued presence;  for example, if Japan were to unilaterally resign from a game of Axis &amp; Allies despite the objection of Germany.