I got one of the latest (cheap, WiFi-only) Kindles at Target a few weeks ago. With this cool Moleskine-looking cover available from M-Edge (I tout the cover because it's super light and I love the way it looks). I had a Kindle 2 that I sold when I got my iPad because you can read everything on an iPad. I bought the replacement because it turns out that just because you can do something doesn't necessarily mean you should and also because I was engaging in retail therapy necessitated by being blizzarded in one too many weeks. Don't judge me. I bought the original Kindle because I was swayed by the e-ink, and one main factor in buying another one is that the iPad gives me a headache if I read it for very long. If you don't read much, this probably isn't an issue, but I read a lot, lot. I never did find the iPad prohibitively heavy, I mean it weighs a freaking pound, but the Kindle is airily, breathily light.
Cool bonus: if you have the new Kindle 3, you can get free delivery of your Instapaper articles (free with use of the @free.kindle.com e-mail address and only over WiFi): instructions here. The articles arrive in a periodical digest format with back-and-forth paging, nagivation to previous and next articles, ability to save highlights and notes, and in general everything a regular periodical would give you. This works well for me because I fly through Twitter and my RSS feeds, sending a lot of stuff to Instapaper, and this system dumps everything onto my Kindle in the category of Things It Will Take Longer Than 2 Minutes to Read. I love Instapaper. If you're not using Instapaper, well...you should.
Anyway. You wouldn't think you'd use both an iPad and a Kindle, but I actually like having both. I'll like it even more if Apple dickishly enforces in-app Kindle purchases for the iDevices Kindle app, but that is a rant for another day. If for no other reason, I like the Kindle because I can take it to work and other places I wouldn't necessarily want my iPad: I would mind the theft of a $140 device much less than that of my iPad.