I have been reading PDFs on my daily reader. I have been mostly satisfied with it.. the pdf files I've been reading are predominantly text with an occasional picture thrown in. Instead of the zoom feature, sometimes I found viewing them in landscape mode to be very useful. Also, like scion mentioned, the margin crop feature was also pretty cool.
I've been trying out the two page layout... of course, you cannot use it for all PDFs... but a neat feature nonetheless...
Good luck with the PRS-900, this is my first e-reader and I'm quite happy with it so far !