I have a Sony eReader. It's nice when it works. Sadly, however, I've run into problems with it. Even with all the system updates, some books just WILL not work on it, even when they should work fine. My sister, who also has a Sony eReader, has had similar problems.
The thing is, it's a great reader. Very low power usage, light-weight, and the screen is comfortable to read on for hours. The page-turning time is responsive and it comes packed with 6 different dictionaries which allow you to look up pretty much any word in English, Italian, German or Spanish. You can adjust font sizes, page layout, and it can read PDF files reasonably well. It's better than the iPad, because it's super light weight and it only uses a very tiny amount of power to refresh or change the page display - one charge can last about 3 weeks of moderate use, and even longer. Storage is more expensive - but hell, if you're just storing books, the SD card that comes with it is more than enough (it can hold over 2000 books. Not even I have that many books I like to read).
But, there are problems with newer books, even in the same format as older books, just straight up failing to work. The Adobe Reader Library Software which you use to put the books on it is a right royal pain to use and sometimes will just not recognize the DRM on books you have paid for.
When it works (and it works for most books), it's a good experience. But there is nothing more frustrating than buying an Ebook you REALLY want to read.... and having it fail utterly when you try to read it.
For the record, the book that doesn't work with my Sony eReader is "The Better Angels of Our Nature" by Steven Pinker. It's a great book that examines the rate of violence and murder throughout history and discusses possible causes for its decline in developed nations. And it doesn't work on a Sony eReader. I've downloaded the book multiple times, I've cleared it, I've FORMATTED my eReader, I've made sure my eReader is up-to-date in terms of its firmware.... it just refuses to work. It only says "PAGE ERROR"!
Support for it has also been pretty crappy. Despite numerous problems, Sony only very rarely updates its software and they have been very unhelpful answering my questions (I have about 6 emails only stating "We'll get back to you", only they never do).
So, if you want to get a Sony eReader, know that you'll get a technically impressive reader, with some support and compatibility and DRM issues. It really is a GREAT reader, on a technical level, but it can be extremely frustrating to use at times.