I did once, possibly even more than once, say that if a writer seemed to be slacking off in getting the next book in the series for me, that I should be able to stalk them and ask about it. Now, in some of my variations of this plan, I was going to offer to chat with them, if there were any roadblocks that a sounding board could assist with, or offer to help with chores and such, if that's what was keeping them from writing. (If, you could see my apartment, you would find that even funnier. Although other people's mess can sometimes be easier to deal with.)
Well, Neil Gaiman is here to set me straight. Writers are not the reader's monkeys. (Gaiman may have used a different word.) Reader's pay for a book, they get a book. the next one is not a contract until the reader buys it.
So, I'm sorry - although hopefully I get credit for, you know, not actually carrying out my plans. Although, series writer's I would suggest that, while clearly you can't wrap everything up, maybe don't end on a cliffhanger.*
Hat tip to a number of people, since I ran into this link a few times, including Abriendo Puertas and on Marjorie M. Liu's blog.
*I read one book that ended with one character asking a question, and I have to say, I was so annoyed I decided never to read another of that series. So perhaps that problem takes care of itself.