I know what you mean about shipper fics - or, at least, bad ones :). If there's Character A / Character B, who had no hint of a romantic pairing in the original source material and exist only as a fan 'ship, then you can have 1) a story in which A and B are both in character, in which they interact with each other (sexually or otherwise) in an interesting way, and in which you might learn something new about A by seeing how he/she reacts to B. Or you can have 2) a story in which A and B are thrown together through some really contrived plot device, get overtaken by a Magical Shipping Field and fall into each other's beds. 1) I like to read. 2) gets tedious, because the author can't hide the fact that A and B could be anyone, that it's all about the sex and not much about the characters.