I guess it just depends on how I feel about the anime. As an example, last season I watched Space Dandy 2 weekly, but I would skip Rail Wars for 3 or 4 weeks then watch them all at once. For older anime, I would say I don't really marathon it either. No matter what I'm watching, even if it's something that I'm really in to, I don't really like to watch more than 3 or 4 episodes in one day. Anything more than that and I tend to get tired of watching and I'll lose focus.