You can count the number of devices supporting the Bluetooth 4.0 standard right now on the fingers of one hand. These include the 2011 Mac Mini and the MacBook Air, while the iPhone 4S is the first phone to support the standard. So what does Bluetooth 4.0 offer over the earlier versions.
Bluetooth 4.0 has two major advantages over earlier standards, first is BLE (Bluetooth Low Energy), a low-energy and low-latency mode, second is that it can wake up other Bluetooth 4.0 devices and do no-code pairing. Nevertheless, it remains backwards compatible with all earlier standards, so you can still connect all your legacy devices.