There's really nothing all that new or ground breaking in the Kindle. The biggest thing that Amazon brought to the game was brand recognition. The average consumer has never heard of iRex, Plastic Logic, Bookeen... etc. They have obviously heard of Sony, but Sony never really put any advertising push behind the PRS line of products. Everyone has heard of Amazon though, and now most people think of the Kindle when you say "eBook reader". The device itself isn't really any different than the others.
If Sony or Barnes and Nobles want to make a serious run at it, then they need to capture that same consumer awareness of their product brand names that Amazon did with the kindle.