Since I am a Kindle junkie and happen to own 3 versions of the kindle (I have yet to shell out the dough or find it even remotely necessary to buy the DX yet) I thought I would give my reviews on each.
Kindle Version 2 - much more streamlined but doesn't have the removable memory card so you can't transfer books or improve the storage. Uses 3G whispernet to download books. This version I found very durable. It is thinner than version 1 but also bigger. The buttons are in much more convenient locations and I didn't find myself accidently turning the pages. I have a silicone cover for my version 2 kindle and it has held up really well.
Kindle Version 3 - smaller and more light weight than version 2 also much more delicate. I'm actually a little afraid of it. I didn't necessarily need a new kindle - version 2 was fine, and I actually really liked it but I was lured by the black color of the new one (silly I know). I ordered a cover because after the 2nd day of having this one the screen broke (not sure how) and I had to have it replaced. I'm actually not sure if I like the smaller size or not I think I'll have to get used to it. My kindle 3 is wifi only so I have to be near a hotspot with wireless internet access in order to download books or access the store, unless I want to hook it up to the computer to download books which is kinda redundant since if I can download books from the computer I must have wifi. The e-ink seems to be darker on this one or it might just be my imagination and the pages are milliseconds quicker.
Anyway the jury is still out on Version 3 I like the lighter weight but I'm a little concerned over how fragile it seems to be. My Kindle 2 was very durable and has been knocked off a couch stepped on by dogs and has weathered the storm, I'm not sure version 3 would fair as well but I guess time will tell.