Well I've seen it suggested many times, and often wondered myself. I've finally gone and created this table. My source for the USCF ratings probably isn't the best, I have no idea what year they are from. I couldn't find anything on the USCF site in my few minutes looking. I also couldn't find anything on the AGA site.
For what it's worth, the numbers line up closely with what I intuitively guessed they would be.
You can get the AGA data by going to the ratings tab and downloading tdlist.xls. All ratings are there and you can get the percentiles yourself. Just be sure to exclude old ratings.
Thanks, I didn't consider just getting the entire list. I've updated the page with AGA data.