Eric von Hippel, a prestigeous professor at MIT Sloan School of Management, has focused his research on developing strategies to identify new ideas and innovations systematically and quickly. He coined the term of "lead users" and pioneered the thinking of user innovation, as opposed to the conventional view of manufacturer-centric innovation in his well known book, The Source of Innovation. Another book from him, named Democratizing Innovation, has documented how the internet and improvements in computing have changed the innovation process. Now users have much more power.
Since I have neither read the books entirely nor engaged in exploring this as far as professor Hippel and his students do, some of my doubts below are quite lay.
Well, it seems to me that "users" can be the (or may be the only) source of innovation, particularlly in the pre-manufacturing stage in human history. Although some of his researches have shown to us with convincing evidence that the innovative ideas originate from the experiences of users, intuition still tells me that innovative ideas are quite possibly coming from those people with professional knowledge who can benefit from commercializing those ideas. Manufacturers can think as creatively as users, sometimes they themselves are users. Since we can not easily compare the magnitude of different kinds of incentives confronted by users and manufacturers, the real source of innovative process is still hard to reveal.
If we can dichotomize innovation into radical and incremental innovation, then my proposition would be like this: users may serve as a major source of incremental innovation while professional manufacturers can mostly bring forward radical changes.
A final point. As to whether the innovation process is manufacturer centered or user centered, it likes the old debate of whether demand creates supply or supply has its own demand.