I like to see these independent characters, who always deal with their own stuff, interacting with characters from another location who are now asked to deal with the first characters' stuff, too. So what about books? I've seen it happen a few times between a single author's multiple book series, as well as two or more authors bring their characters into a joint venture. I like it, especially when I've read the previous books that are mentioned. It's like an ah-ha moment when you recognize a character you already know in a place you didn't expect to see them.
With all that being said, I'm considering a crossover with characters from my Liz Baker series in my new Penny Montague series. As I'm writing this first book I feel a natural progression toward making mentions of the vampires and werewolves currently residing in the north Georgia mountains (i.e. Liz and Monty). Penny resides in the Atlanta area, but you'll find her on a mission that leads her farther north. Soooo.... maybe?
What do you think about crossovers in books?