7.1 indicates 7 speakers, comprised of 3 in front (L+C+R) and 2 surround sides plus 2 surround rears, and a subwoofer. No music or movie material to date utlizes all 7 speakers discretely, though some receivers and pre/pro units will direct a matrixed signal to these 6th and 7th speakers.
Several notable makers offer 7.1 receivers that include 7 internal amps to drive each of the 7 speakers. It is their decoding software that stretches the sound into those 6th and 7th speakers. Note that the new Dolby Pro Logic II only provides info for 5.1, even though some receivers will place sound in the 6/7 speakers.
My two cents? A decent 5.1 setup is mind boggling (just play the DTS version of Saving Private Ryan to hear what I mean).
As one well know AV critic once said recently, "Let's give all the media producers a chance to produce music and movies using 5.1, they're just getting comfortable now -- why should we all of a suddent move the goal line to 7.1 before they've even had a chance to score using 5.1??"