Summary: For the most part, I like the reader. It handles epub, PDF, and has internet support. Downsides: The browser isn't supported widely as most mobile browsers are today. Text sizes need to be re-tweaked. They range from hilariously enormous to too tiny to read. PDF reading is painful; it's the margins. The reader can zoom in on a page to eliminate the margins, but when you change pages you have to redo the zoom.
Summary: I like the hardware, but 1) The software is cumbersome. For example if you subscribe a newspaper and you want to download a previous issue, it takes several steps. Another: try to look for a book that you don't know the exact title of the full name of the author. Your experience won't resemble at all the one you have here at Amazon. It is so ridiculous that many times I come here to get that information! 2) Sony customer support sucks! For example, I subscribe the WSJ.
Summary: I tend to read a lot of scientific journal articles and books from research publishers such as ACM, IEEE, and Springer. I also find myself knee deep in reading computer specification documents as well. Almost everything I mentioned of course, is in PDF format, which the Sony and Kindle DX both support. The first thing I put on the Sony PRS 950, a PDF of the UEFI Specification, I got an "Invalid page" error and couldn't change pages.