Originally Posted by epiphany
I'll offer my 2c although I've only owned a PRS500 and 505. If you can get access to the Sony eBook Store this is a real benefit. They have a lot of newer books you wont be able to find in other formats (except from Amazon).
I must respectfully disagree. The overwhelming majority of eBooks are released commercially in all the major formats - Kindle, Sony, MobiPocket, and PDF/ADE.
A device which supports MobiPocket gives you access to the widest range of eBook stores, compared to the other formats.