Usually I'll read all at once, but it depends on the series! If it bores me at any point, I'll probably put it down and resume later, if I'm at a friend's house and it ges shoved at me by my "Sensei" (one of her older sisters xD) I'll absolutely have to read it on-the-spot (overprotective of manga, you see) if I'm at home, I'll read them leisurely, usually without a break.
Honestly...as much as I love manga, I'm kicking out of the habit of manga-reading, and it just isnt as appealing as it used to be. Same with anime.
I can't get rid of it completely, as I obviously just started here XD