Along this line of thought, since "micro" means pretty darn small, how about going to the molecular/atomic level and using something along the lines of the most basic element? The general symbol for the hydrogen atom (however technically inacurate it is) is a big ball with a little one whizzing around it. This basic symbol also generally looks like a planet being orbited by a moon, much like our own, which is also what bittorrent clients do..... connect people together over the whole planet who have something to share. The same symbol could show both the compactness of our favorite client and it's basic world wide functionality. I'm sure a µ could be added to it somewhere. Unfortunately, being the most non-artistic person in the universe (those that would admit to knowing me personally would probably say I was more autistic) I have absolutely no idea how one logo/icon could convey both messages. I just had the idea and thought i'd throw it in the ring.
