Google released the world's largest corpus and did us a favor by analyzing it for n-grams. For example, they found that the phrase "serve as the initial" was over a 100 times more common than the phrase "serve as the insurance". [1] For $150 you can buy the 24GB data set yourself, so it's a fair assumption that makers of password crackers could reliably guess common phrases first. [2]

[1] http://googleresearch.blogspot.com/2006/08/all-our-n-gram-ar... [2] http://www.ldc.upenn.edu/Catalog/CatalogEntry.jsp?catalogId=...