In one of Lisa Gardner's books, a character notes that in Rhode Island, locals go and request plates with letters that are meaningful to them and low numbers. As someone who has family up near the Rhode Island border, I would not have been able to tell you that prior to reading it, but it made perfect sense once I did, and helped with the setting (hopefully for Rhode Islanders too).
I actually didn't believe the first person that told me the black Delaware plates were inherited. (It turns out that now you can get authorized reproductions.)
But, I absolutely had noticed that Virginians, in addition to having a plethora of plates to choose from (much like Florida), are big, big fans of vanity plates. One co-worker, when I discovered she lived in Virginia, I said, "Oh, so you must have a vanity plate." (She did. Seriously, play this game next time you meet a Virginian. Then ask them which plate they got.) So, I am unsurprised to hear that Virginia leads the nation in vanity plates.