Does impedance matter?

In all my post readings, the #1 question category is the 'Does It Match' question. This is usually addressed as a speaker / amp question.
Most responders start with impedance.
Of all the things to look for in a speaker impedance is down the list. I have looked at at many speakers measured by reputable testers. 8ohm 'nominal'? These guys are all over the place from 3ohm in mid frequencies to 20 ohms+ at resonance. Some are 4 or 5 ohms from 200hz to 1khz...prime musical turf.
Is it easy to drive? Well, it's an 8 ohm speaker, so it should be. Not so fast, there. This is only part of the story.
Please check out this link::http://www.hometheaterhifi.com/technical-articles/228-a-secrets-technical-article.html?start=1

The Smith Chart is a fine way to visualize the quality of load a speaker may actually represent.

When looking at a speaker then, it is important in evaluating the load it represents by not only the impedance, but the inductance and capacitance as well. As voltage leads or lags current, the strain goes back to the amp.
Please see this link for an explanation / details.
http://sound.westhost.com/patd.htm

Just watching Diana Krall in Paris on the TIVO.