What could I expect to hear from a Class A amp?

Al - read also this http://stereophile.com/news/10065/

Class A is probably the best SS. The real question is what is the best amp for the money one has assigned to spend. For me it was class D - maybe not at the level of top class A amps but way better than my previous class AB amp.

The usual total harmonic and intermodulation
distortion figures do not reveal the abrupt output stage distortions accurately
because of the averaging factor involved in such measurements. A spike of
crossover distortion may reach 2 per cent, but if it occurs only over 5 per cent
of the waveform, it averages out to a respectable 0.1 per cent distortion
figure.

What he doesn't say which is important is that the crossover distortion is
fixed (it is not amplified as you crank up the volume, at least that is my
understanding) - therefore Class A becomes critically important at low power
output => this is what makes designs with sliding bias or several stages that
include a Class A stage attractive. (it allows distortion to remain low at low
output levels or quiet passages but then still gives you the ooomph needed
for loud passages....the crossover distortion is less critical during a loud
passage as it is a relatively small amount on a good Class AB design
compared to a big signal output)

This also makes an active speaker topology attractive. Since the distortion is
high order then some of the worst stuff is going to come out the tweeter. In a
biamplified active speaker design you simply feed clean Class A for the feeble
power requirements of the tweeter whilst you can power the mid/woofer with
a beefy Class AB design without much worries over high order harmonics or
intermodulation distortion being all that audible

Shadorne: Correct as to the unamplified nature of crossover distortion. It is only the ouput, or final, stage at which the bias point is placed near cutoff and saturation, respectively rather than centered - in a class B amp. How hard that stage is driven makes no difference as far as the amplitude of the crossover distortion since there is no amplification following that stage. But since the excursions will be greater away from the crossover point, when driven harder, any change at the crossover point (which will be insignificant anyway in an AB design) will be a smaller percentage of the overall signal. Hence, at low values of output signal any such distortion would be a larger percentage of the output signal. As to your comment regarding active speakers - absolutely true - it always makes sense to design the electronics for the load and the more known about that load allows for an easier design with less compromises.

It would be nice to know of non-Pass Class A amplifiers that perform well, and why so. Bearotti asks about Krell. At this point I am curious in just about anything Class A. The whole discussion thus far is very helpful to me as a Pass XA60.5 owner, but thus far continues to confirm what's heard through the months, in that nobody remotely comes close to Pass Lab on Class A amplifiers. Otherwise there would have been well-informed and fairly objective challenges left and right.

It would be nice to know of non-Pass Class A amplifiers that perform well, and why so.

ATC make amplifiers with what is probably a sliding bias - you get 2/3 power Class A before it reaches Class AB operating point for the final 1/3 power. I have not compared them to Pass but ATC are relatively unknown as an amplifier manufacturer whilst Pass is legendary. You are safe sticking with Pass, IMHO.