Speaker wattage question

Chris, Lots of good information above.  Just to expand on a couple of points - music in general has relatively little energy at the frequencies handled by the tweeter and these drivers are not designed to handle a lot of energy.  Once an amplifier is pushed into clipping it begins to generate harmonic distortion.  The distortion products relevant to this discussion are caused by the summing of fundamental frequencies in your music which produce higher frequencies.  Harmonic distortion is present in all equipment to a (hopefully) small extent but in most clipped amplifiers this distortion increases dramatically.  Your speaker's crossover dutifully routes any of these signals higher in frequency than the crossover point to the tweeter, increasing the likelihood of damage.  This is why the interaction between  your amp and speakers (impedance and negative phase angles), especially in the frequency ranges where most music - or the music you listen to - resides and why it's important to know your speakers impedance characteristics (see JA's measurements in Stereophile) when matching an amplifier.  As has been said many times, far more speakers have been damaged by pushing an underpowered amp into clipping than by playing a powerful amp loudly.  Dick