The statistics of shot durations in 150 films from 1935 to 2005 were analyzed. From about 1970 to the present, the power spectrum of shot durations in individual films has tended to become more like pink noise (power ~= 1/f). Also, autocorrelation shows that the lengths of nearby shots has become more and more correlated.
The authors, Cutting, DeLong, and Nothelfer, speculate that the pink noise bit is being driven by some process that is related to attention, since there are some other results (which they cite) showing the relevance of pink noise to attention.
However, IMDB ratings were not positively correlated with the pink-noise-ness of the movie (partial correlation with release date factored out).
Incidentally, this guy did his PhD thesis on cognitive science explanations for film editing techniques.
James E. Cutting, Jordan E. DeLong, and Christine E. Nothelfer. Attention and the Evolution of Hollywood Film. Psychological Science February 2010 , first published on February 5, 2010 doi:10.1177/0956797610361679.