Dual processors an advantage?

I am a new arrival to the G4 and OS X world, having had the opportunity to purchase a used dual 800 MHz Quicksilver. I was reading reviews dating from when dual processor G4s first came out. The reviews said that dual processors didn't have that much of an edge over the single processor models (and little to none over models with a slightly faster single processor) because most software wasn't designed to take advantage of the second processor. Unless you were running high-end packages specifically tailored to dual processor use then your computer was bascially a single processor machine.

These reviews were written back when these computers were as likely to boot into OS 9 as into OS X. My questions is, does OS X (e.g., Tiger) compensate for deficiencies in software design as regards to using both processors? Does it make use of both even if the software wasn't designed to do so? Does it do this even if a program is running in Classic?

I'd like to do some video processing, though mostly using freeware/shareware packages. This is pretty processor intensive and I'm wondering if having a dual will be an advantage or if the second processor will just be sitting there unless I go for higher-end software ($) that specifically uses both.

Thanks,

Brian