I use a S*ny eReader, much the same thing without the cellular connection. I got used to the slow refresh rate pretty quickly, you eventually get so you can push the next page button just before you get to the end of the page and finish reading as it refreshes. Once you're used to it it's faster than turning a physical page. The menus are always really slow but I only tend to hit those between books so it depends how quickly you read as to how annoying that is, I think the kindle is a bit faster on that score.
I don't tend to buy books for it, because I don't like the DRM and ebooks tend to be more expensive than physical books but I have no particular moral issues with ordering the book on Amazon and downloading and reading it while it's being shipped, and that tends to work well. There is also a lot of free stuff out there so there is always something to read.
My biggest issue is probably that airlines want me to turn it off during take off and landing. (And then rub it in on night time flights by announcing that the lights will be off for takeoff but if you want to read you can use the overhead light.)
I'm not a fan of the Kindle, Kindle editions from Amazon seem overpriced (They seem to just be priced along with the hard cover even when the paperback is released) and the keyboard and wifi/3g connection never seemed that useful to me. The lack of storage also seems like it'd cause problems. You don't need much space for books but if they're only going to put 180MB of flash in (usable anyway) then at least they could have an SD slot. I think my e-reader has built in storage, but with both SD and MS slots I don't really care (64GB of flash would be excessive, but I like that it's possible).