It's a little later than I promised, but here are a few graphs looking at the position of some series on the Amazon Top 50 charts during 2010:
(You should be able to click on a graph to get a larger version.)
(Remember, a title in position 1 on the chart gets a score of 50, so higher number = higher on the graph = better.)
This graph is fairly typical for a franchise with a movie based on it. Interest in Scott Pilgrim starts in March, then intensifies in June. Unfortunately, June is also when Amazon decides to reclassify vols 4 & 5 as not being graphic novels for a time. A sizable discount keeps interest high through the autumn, until November when prices return to normal Amazon levels and interest softens a bit.
Diary of a Wimpy Kid:
The Walking Dead: