re: "...don't even know what the Harmonic balancer is. I looked it up and I get the crankshaft pulley. Is that what you're talking about?..."

Yes, that's the harmonic balancer. It's a hefty pulley, and it's in two parts, an inner (bolted to the crankshaft) and an outer ring (which drives the belts), and they're joined, using some adhesive, by an intermediate ring of rubber. The adhesive eventually fails and lets the inner ring spin (driven by the engine) while the outer ring is held behind by the resistance in the accessories (water pump, alternator, A/C and p/s), so they don't turn as fast as they should.
Additional note: since the ignition timing mark is on the outer ring, the timing mark wanders if there's slippage because it's no longer synchronized with the engine's timing belt and other shafts.

re: "...No one seems to have mentioned the bushings for mounting the alt. I imagine it would be a good idea to replace those as well if I should change out the alternator...."

I think you should consider the bushings if you find that the belt is slipping and you can't get it tight enough (to prevent slipping, squealing) without excessive tension (allowing less than a 1/2 inch flex on a segment). The alternator isn't really held rigidly in place, but depends on the bushings for such stiffness. I personally have changed all of mine (all accessories) to poly, but a fresh rubber from Volvo (don't use other brands) are OK, too.

Good luck.