You won't be doing it without realising it - at least it's very unlikely.Also, you state running multiple processors does no good unless you are running heavily threaded apps. I don't know what that is but, maybe in my head I will be doing that without realizing it. Do you mind giving me an example?
The only multi-proc machine I use on a regular basis is my development server where I work - that thing can take hundreds of hits on a very very CPU intensive server application without falling over (and hundreds of thousands on a normal one.) I need that sort of capacity for stress testing how my code holds up against that many users, and in this case having more than 1 powerful CPU is a definite advantage.