Never ones to back down from a challenge the Dark Forces Team (DFT) have created a neat little utility to allow one to transfer files between phones or devices using just Bluetooth. You can even send over XAP files for installation of Windows Phone apps giving users yet another option for file distribution.
The bad news is you'll need a fully-unlocked phone meaning dev and interop devices need not apply. That also limits this currently to Gen 1 devices (as you can see initialization fails on the Titan for obvious reasons).
Still, it's an impressive piece of work and hopefully it will lay the ground work for future hacks, assuming Microsoft doesn't give us the function first.