There are a lot of possibilities to extend the application. The most interesting would be to connect information from other sensors with this information:
Location-Information: It would be possible to see on a map, where you discovered the Bluetooth devices
Motion-Sensor: With access to the motion sensor, it would be possible to search more often for other devices, when someone is walking. At the moment the application looks every 2 minutes for Bluetooth devices nearby. For example the IPhone or the Sony Ericsson W910i has such a functionality.
Related work BlueJackX - Same functionality as Bluetooth Logger, but this only works on Symbian-Smartphones. Blooover - Does no logging, but works also on Java enabled cell phones and is used to find weak spots of Bluetooth devices
For desktop computers there are tons of applications, so I won't list them here. Check out NetStumbler for Windows, which is very popular for Wardriving.