I purchased this during it's last appearance just before Christmas as a present to myself. I also own a Gen 1 iPad, Gen 2 13 inch MacBook Air, Iphone 4, Gen 2 7inch Kindle (3g) and the Fire.
Just as i had hoped, the DX has become my go to reader for sessions > 2 hours at home. Despite it's size, it is lighter than i thought it would be (lighter than my ipad), it is comfortable to hold sitting or laying down and the larger screen means more text and less page turning which makes it feel a bit more book-like. The newer e-ink is noticeably better than that of my 2nd gen Kindle, which will now be relegated to my traveling/outdoor kindle due to its smaller size.
3G on these devices is a must, i can't tell you how many times i've been browsing the books at the newstands in the airport and have simply popped open the kindle to make the purchase while sitting in the plane prior to takeoff...its very convenient.
My iPad is my primary couch/bed surfing device. Nothing compares to the smoothness of the iOS interface and Safari for a web surfing session. I'm also heavily invested in the Apple Appstore, so they kinda have me locked in.
When i need to be a little more productive on the couch, the Air comes out, instant on, super light, decent size screen and keyboard...nuff said.
The Kindle Fire....i consider it a toy currently and use it the least. I mostly bought it for the smaller form factor to take on trips so i can leave the ipad at home with the wife. The general interface is OK, the Silk browser is not nearly as smooth as Safari, i find my self having to tap links multiple times to get them to open, scrolling and tap to zoom doesn't work as well or as smooth as on the iPad, maybe in a future update...(i'm current with my updates, but its still got a ways to go). Current lack of apps annoys me a little...mostly the inability to get the CNBC realtime app, but this will change with time.
Folks say 'why not get the Fire at this price', Fire vs the DX....they are really 2 different devices imho. If you read books, get a regular Kindle, if you need a cheap tablet, the Fire is OK. Kindle readers are a joy to read on, the Fire, not so much. As a tablet, it's OK, but the Ipad is still the clear winner.