Recently a friend complained about the seating arrangements at her cousin's wedding. She'd attended with her parents, her brother, and her sister, but they'd been seated at different tables -- parents at one, her siblings at another, and her at a third. She wished they'd been seated as a family.
I found that interesting, because my number-one dislike at weddings is being seated with my in-laws. Don't get me wrong -- I love them dearly! But we end up having the same conversations (or disagreeing over whether the kids need to eat their peas). I like sitting with people I only sort of know, or that I don't see often. Sometimes I'd rather sit with a complete stranger -- at least the conversation is fresh! My MIL and FIL, on the other hand, really love being seated with the younger generation. I think they like their energy -- and they often get seats with the aunts and uncles they already know well.
All in all, you can't please everybody. But how are you going to divvy up the seating? Check out our Wedding Etiquette Advsior for more answers to your trickiest questions.