Could multiple advisers mean that it might be easier for you to get funding? (since you're not just limited to one person?) Could it also mean that you get more overall input in your project (the input of 3 different people), and that maybe your project will be geared in a way that it's "interesting" to more people, and consequently might also get more citations that way?
They might pull your project in different directions, but how much is this really a concern?
And what about the special case where they explicitly expressed the desire to interact with each other more through the student? (this was actually the case in my situation).