Most times, innovation is incremental - a pyramidal structure of thousands of small ideas, all piled one atop the other. Rarely do we see great leaps, where an idea is so striking that it changes a paradigm.

A patent benefits an individual entity (person, corporation, whatever) by allowing that entity sole use of the patented process/product/whatever. It also, as a side effect, hurts society - the patented concept is unusable by anyone but the patent holder, except under license. This adds a 'parasitic drag' to the free flow of ideas, and drives up prices for services and items based on the patent.

and now I have to go to a meeting, so I'll have to stop here ;)