I give the 650 an A+ for "reading experience" for novels or other text-heavy ebooks.
I give the 650 an A+ for saving lots of money in accessing free books.
I give the 650 an A for long battery life.
I give the 650 (and probably other similarly sized eBook readers too) a
D- for reading books containing a lot of maps, photos, diagrams, tables, footnotes, etc. It is just too awkward to navigate from one section of the book to another
I bought an eBook reader because:
(1) It seemed I'd be able to save a lot of money (getting free classic books from Project Gutenberg, free books from public library, or at a $10 discount over new hardbacks). This has proven to be true. I've already read several free books from Gutenberg (www.gutenberg.org) and the supply is endless. I haven't bought any eBooks yet (other than the lord of ring series and steinbeck collection to use my $50 gift card).
(2) I have poor eyesight and the adjustable font size appealed to me. WOW!!! It is very easy to read on the Sony. In addition to the large font size, simply being a flat reading surface eliminates the shadows you get with real book. Also, the Sony stays open when laying on a table so it is very easy to read hands-free (while eating, poor manners, I know, sorry).
Regarding Sony vs Kindle or Nook (or IPad thingy).
I deliberately picked the Sony because it did NOT have internet access. I DO NOT want to be distracted while reading. I have enough ways of accessing the internet - I DO NOT NEED OR WANT another one.
I also picked the 650 because of its touchscreen interface. I love it. At my local Best Buy I tested the Nook and I thought the Nook interface was very confusing. Maybe I'm dense but I was completely confused by its two-screen approach (big eInk screen for reading and little color screen for some navigation.) I played with the Kindle (it was not a live unit) and it felt very cheap and I didn't care for the internet access.
Overall I like the Sony interface - my one big complaint is the absence of a direct 'back-up' button when you are accessing footnotes or some other part of the book. You can use the 'history' feature. But I would think that if you access a footnote by taping on the footnote number, you should be able to return the original paragraph by tapping on the footnote number again. That needs to be fixed.
I also like the size of the 650. It is light weight, easy to hold and easy to turn pages by swiping finger or pushing the buttons. It is small enough to easily fit in the inside pocket of a jacket. It also fits (I better be careful though) in the back pocket of my jeans. I did not seriously consider the IPad because of its large size, high cost, and shorter battery life. Though it is a beautiful thingy).
I've been using the Calibre program to manage my eBooks rather than the default Sony application. I bought the device - I didn't want to get married to Sony (or to Apple).