I gave myself 50 minutes, and it took about 60. Answers: 1) Yes and 2) doesn't seem to be.
For me, it was more a data-map-time challenge to myself.
Below are my quick proof-of-concept (or no proof!) maps. There aren't any legends on them yet, but the color gradients indicate the number of restaurants getting that grade as a percentage of all the restaurants in the zip code (0-2-4-6-8-10%+).
See any patterns? I don't ... yet.
But I did learn how to take a whole bunch of records and run a couple of aggregations and merges in Fusion Tables to actually visualize them. In about an hour.
UPDATE: Because some folks have asked: The sum includes all restaruants in the zip code, including those with "Pending" grades and those that haven't been inspected, which is the vast majority in many zip codes.
UPDATE2: Pulled together key parts of the twexchange using Storify, below.
UPDATE3: Steven Romalewski's look at a Wall Street Journal story let me to realize that even though only a small fraction of the restaurants in the data set have letter grades, almost all of them have a "score" -- which means I ought to re-analyze based on that column instead (which I'll do tomorrow).