A recent article (March 2015) entitled 'Attention decay in science' concludes that "the exponential growth in the number of scientific papers makes it increasingly difficult for researchers to keep track of all the publications relevant to their work".
"Consequently," the say, "the attention that can be devoted to individual papers, measured by their citation counts, is bound to decay rapidly". The risk here, in a time where the number of publications is booming, is to overlook important data and theories due to the much larger pool of papers among which attention has to be distributed and the limited capacity of scholars to keep track of it.
Apparently, the citation rate of papers increase just after publication to decrease rapidly after a few years. The authors specify that "the decay is also becoming faster over the years, signaling that nowadays papers are forgotten more quickly. However, when time is counted in terms of the number of published papers, the rate of decay of citations is fairly independent of the period considered. This indicates that the attention of scholars depends on the number of published items, and not on real time".