-bcgirl, great question, interesting thread.
My first was a kindle keyboard 3g, and I still use it on hot summer days by the pool. I figure if I drop it in the water...oh well. But I havent and it still works as smoothly as the day I got it.
My second was the original Kindle Fire, followed quickly by a Samsung Gtab 10.1. I dont use either of those any more for books because the "flashlight-shining-in-my-face" effect cooks my eyes if I engage those for a long reading session.
My next ereader, my fourth, is a Kindle Paperwhite and I love it. I read with it pretty much daily. For finding books, getting them quickly and pure reading enjoyment I score it an A+.
Curiosity and a desire for a really portable ereader led me to an impulse purchase of the kobo mini. So impressed was I with this little guy that I went out and bought a Kobo Glo so I could synch the two and read the same book in the dark. There are some Kobo features I really enjoy and switching back and forth from Kindle to Kobo is kind of a kick.
So, my final tally is 6. I wont buy another traditional back lit tab to read on but I may one day go for a nook, if they update their dedicated ereader. What would be really cool is for Kindle, Kobo, or Nook (or anyone really) to come out with a ultra portable glo/paperwhite type screen. I would buy at least one of those!
By the way, my count doesn't include the ereaders I've bought my wife - guess what she is getting for Christmas?