Here is an example of using the Notch Filter on a 40 meter QSO. There was something causing a spike (I suspect RFI) right in the middle of the LSB QSO. So I used this to easily eliminate the spike making it easier to hear the QSO.
This was a quick demonstration for a friend.
I was using an RTL-SDR tapped into the IF on my Yaesu FT-857D, running HDSDR on my Windows 7 machine.