I have not yet purchased a dedicated e-book reading device and with so much developing now I'm not in a hurry anymore. Not in a hurry to the point where I picked a Verizon Droid smartphone as my toy for the year.
However, of all the current choices I really like what Astak offers much more than Sony due to the user replaceable batteries the Astak units have. After a year of use both my cell phones and mp3 players always have a severe downturn in how long the battery will stay charged. The phones I replace the battery and the phone is like new again. The mp3 players I suffer with or buy another cheap one. I used to work in a cubical so everybody had an mp3 player going all the time to block out nearby meetings and phone conversations so the device lasting shorter and shorter a time was quite noticeable. My personal policy these days is that unless an electronic device has a price tag of $50 or less I won't buy it unless the battery is easily user replaceable.
The issue of having to purchase a cover and A/C charger is another strike against the Sony for me.
Good luck with your choice!