In my journey of trying to find my eReader (Eventually bought the DX)
I found that I would have gotten the 505 if PDF support was the most important thing to me.
I was able to try a 700 and a 505 with pdf's.. The 700 was nice.. but the contrast was too low.. I also found most placces I looked the 700 was going for 349-369.. Borders books (in the US) had it for 349.
Ultimately I went with the DX because it had the larger screen, which I think will help with the PDF's.
Ohh and the type of books I want to buy (Computer based books) are mostly cheaper..