I've only tried triggering a few simple AppleScripts, but it has potential. I've noticed that the iPhone never stops searching for devices (well, the spinner in Bluetooth settings never stops), and this may seriously reduce battery life, but I've gotten inconsistent results at best. Running scripts is nowhere near as useful as a true wireless sync, but it's a step in the right direction.
[robg adds: The linked blog entry contains some pretty useful scripts to run with Proximity.]

