Slow time, time out and vacation
I am currently playing two games against a player who is going to lose both games and who seems to need to take almost three days on every move. He also has used all of his 90 days of vacation, and no doubt will eventually time out rather than resign.
Although I am a premium member myself I don't think the auto-vacation feature is at all fair.
I've kept a list of players who time out. Over the last year or so 14 players have timed out on me. Twelve were slow-timing and losing. One was a genuine time out who sent a polite apology, and in one case I gained an undeserved win against a better player.