Also of interest is the "Harvard Dialect Survey" [1], which gives direct questions and highlights the regional variances. My favorite is "standing on line" vs "standing in line" -- I had never even heard the "on line" variant until I moved to NYC, where it is ubiquitous.
Apparently now there's the "THE CAMBRIDGE ONLINE SURVEY OF WORLD ENGLISHES" [2], apparently by the same individual, but I've only just started looking at it.