Agree with Graham - pdfs are a mixed bag. My Sony PRS505 displays them much better. I download quite a few library books in pdf format so it is important to me (I don't need tech pdfs anymore as I have completed my MA finally). Some libraries are moving towards EPUB, thankfully, but there are still a lot of pdfs out there.
I have picked up a lightly used PRS300 which flows in the same way as the PRS505, and will be selling the EB511 (will upload some photos here at the weekend).
For EPUBs though, it is really good, particularly for the price. They are back at Waterstones again for £129.99.