Bluetooth 4.0 is the latest specification to be adopted by the Bluetooth cabal, which notably adds Bluetooth low energy into the mix, which is designed to allow radios that sip battery like 802.15.4 ("ZigBee") to directly connect to consumer devices.
It sounds great, and according to a search for "bluetooth 4.0 devices", we are swimming in them because they all showed up Q4 2010, however I can barely find more than a single chip (TI CC2540), let alone any consumer product that is BT 4.0. Where are they?