I promised the DDR fanatics over at Aaron in Japan's forums that I'd plug this here, so here it is - Written by Aaron himself, this is a look at DDR throughout the years from Japan's perspective. Starting from 1st MIX's release back in 1998 all the way up to the release of DDR X2 from last year!:

Link to PDF | mirror (Which I'm told is still very much a work in progress, but it's still very extensive in its current state.)

(Also I'm posting this because we weren't able to get the coverage at AI for the epic get-together yesterday, so I hope this makes up for it!...ETA: and Aaron just commented in the thread that he remembered us from back in the day!)