One of my main sticking points about Wi-Fi on my BlackBerry is that it kills the battery when it is not connected to an access point. Say you used it at home and when you leave your house it stays on. Your BlackBerry will keep on wasting battery life trying to scan for a new access point. Currently there are solutions that will turn Wi-Fi and Bluetooth on and off based on your location and cell phone tower but Wi-Fi Disabler has a simpler function.
Wi-Fi Disabler will just turn off your Wi-Fi connection a set number of seconds after it is disconnected from your router. That way you turn it on manually and it will turn off when you leave your house. Personally I wish it would also turn on when you get near your home cell tower but hopefully that will be added soon.
Right now the app is on sale for $2.49 which is a decent deal but the regular $3.95 is a bit pricey for this one trick wonder but hopefully the developer, Ozzy Productions, will either add some more location features or keep the lower price. Otherwise Location Profiler, which is way more powerful, is a better deal for $5.99.