I "binge" watch. I can't stand waiting to see how things will turn out so I watch an entire season at once. For a 12-13 episode arc, that's not a big deal but for longer shows that can take days. Somewhere between 15 and 20 is my limit in a 24 hour period, though. But, if I am watching a long series, I'll watch spend 4+ hours a night as I work my way though it. I usually wait until a series is done before I tackle it for this reason. For the longer shows like One Piece, Bleach, Fairy Tale and Naruto I wait until 30 or more shows have passed before I catch up. Most story arcs (except for One Piece) don't last much longer than 30 shows.
Depends on how much time I have on my hands- usually a handful of episodes at a time. Only once have I sat through an entire series in a single day (averaging out at 3 episodes an hour, skipping the OP/ED).