I have a Sony PRS-600 and I love it, even when it goes into fibrillation once every few months. And I will be definitely be buying a new Sony soon.
The big advantage was when I started using calibre
calibre supports Sony like no other. I hesitate to say this, but without calibre support the Sony is not any more advanced than some other ereaders. I would download a library book, and it would look dreadful. Went into fibrillation for 3 days once and I was on a bus for the first 6 hours of that
and setting up collections with Sony Software when it would condescend to work was tedious to say the least.
calibre developers have provided very good support for many other ereaders. When I bought my mother a kindle 3, developers who had no initial knowledge of the kindle 3 helped me get it set up for her. Now they have even more options and abilities for sorting on the kindle 3.
Don't give up on your particular device you have bought too soon. Quite often (not always) things get better.
Helen