Depends on what you're after. The Kindle is backed up by Amazon's huge catalogue of books, and has a ridiculously easy purchasing mechanism (sometimes too easy...), along with almost fault-free syncing to the iPhone/iPad apps for those 10 spare minutes when I'm waiting for a bus and wanting something to read.

Don't know about the US, but certainly in the UK there's nothing that I've come across that comes even close to the Kindle for my usage patterns - and I'm prepared to pay that little bit extra for that level of usability.