FCC filing last year. But seriously Amazon, $54 for an electronic book... are you kidding us? Anyway, the launch rumored for October 15th certainly looks imminent.
Update: As pointed out in the comments, an Amazon search of "Kindle Edition" responds with 631 books of which a couple dozen can be "auto-delivered wirelessly to Kindle." Alrighty then.
[Thanks, Serkan C. and Ed]