Amazon's Kindle DX is sold out again. Amazon says that this is due to heavy customer demand. It will continue shipping in 4-6 weeks (just a couple of weeks ago, the Kindle DX was sold out, but than it took Amazon only a couple of days to get more inventory).
It might be that E Ink have problem supplying the large 9.7" E Ink display, or, perhaps, there is indeed heavy customer demand. The Kindle DX costs 489$.