[e_modad]

I think warrenmar is referring to the fact a paper's impact can be measured by counting the number of times other authors cite the original paper.

IIRC, Larry and Sergey used that idea as the conceptual framework behind PageRank. Indeed, they were right: the relevance of a search result can be increased tremendously by indexing as many pages as possible and then calculating how many people are linking to said page.

They don't do it like that anymore but that's the basic idea.