I have a third generation Kindle (wifi only). My experience is mostly positive. My kindle does have a nasty habit of rebooting for no apparent reason while I’m reading. It also periodically refuses to wake up necessitating I hold the power switch over to force reboot it.
Other than those two pesky issues, it’s great. While I have purchased several books (and downloaded many more free one) I use a program called Calibre to convert all my old .lit and .rtf books so they’re usable on the Kindle. Since I tend to read multiple books simultaneously (both for business and pleasure) I love being able to have almost my entire library at my fingertips without carrying a suitcase of books everywhere I go.
If if weren’t for the two problems mentioned above, I’d say the Kindle was about perfect.