ZigBee is a newish RF radio protocol at the same frequency of Bluetooh and 802.11b (ISC 2.4GHz). Unlike both of those protocols, it doesn’t suck (power). It’s meant to sip on batteries for months while still being part of a ZigBee mesh. And it seems to be designed to better deal in noiser environments (which the 2.4GHz band is definitely now).
There’s been at least one article in Circuit Cellar about it, I need to re-read it.