It looks like .Mac subscribers are going to get a little more out of Leopard than the rest of us. .Mac's Back to My Mac feature is new in Leopard, and is pretty neat. Basically, it allows you to connect to a remote Mac over the Internet and access files or log into the Mac remotely. I imagine this is being done with some sort of dynamic DNS (.Mac keeps track of your remote Mac's IP address and allows you to connect to it).
There is a video demoing the feature on its .Mac page, so go check it out.