K2: my first e-book reader, went to my wife after the K3 was announced and I just "had" to get one. Initially the wife didn't want anything to do with e-books. (liked the smell of real books, the feel of turning pages, etc, etc....). However, now she "won't leave home without it!"
K3:small and convenient to carry anywhere.
Kindle DXG: I really like it for reading at home while seated in my recliner. The larger form factor is ideal for me. Just a nicer experience than the smaller format devices.
NOOKcolor: OK, just had it for about a day, but my intentions are - reading magazines, reading kids books with my grandchildren. Should be real handy to look up something on the web when I'm in the living room, patio, etc. I'm sure that it will be much more convenient than using my laptop for things like that.
NC also opens up access to formats not supported by the Kindles.
As a side note, even though I'm 63, and use computers all day at work, I do not seem to have problems reading from LCD screens. I actually find myself reading Kindle books on my PC for an hour or so in the evenings before I decide to get more comfortable and go to the living room to read my KDX.