How does the file sharing via MobileMe differ from file sharing using Back to My Mac?
i'm not quite sure what you're looking for here but i'm going to take a stab at it by using the example that i have a MacBook and i have a Time Capsule. when i am at school i would love to be able to access files from my Time Capsule at home let's say to watch a movie i have stored on there because i have a long break between classes and no homework.
with Back To My Mac, i can't do this because my Time Capsule on its own is not considered a machine and therefore can't access files from it using that service at will. this MobileMe will permit that type of interaction, similar to a Back To My Mac, but more like a Back To My Mac Peripheral Device. is that what you are asking?