Goertzel algorithm for tone detection

Came across an interesting algorithm today - the Goeretzel algorithm - which is used to detect specific frequencies in a sample. For example, detecting DTMF presses on the phone. There is a write up in wiki: http://en.wikipedia.org/wiki/Goertzel_algorithm

A SDCC dev list member pointed out that for some applications, it is sufficient to use quadrature square waves to detect/demodulate specific frequencies. I need to look into this more (see sdcc user request list 2009-May-14 from Scott Dattalo). So far, I've come across:

http://en.wikipedia.org/wiki/Detector_(radio)
http://www.commsdesign.com/showArticle.jhtml?articleID=192200456