Djehuty,
Definitely follow their advice of trying it out at a local store. Then even have a working PRS-505 model at many Target stores, and I tried one out there with a bunch of .PDFs on a card.
I'm an academic (a professor) and use my 505 for reading journal articles and other academic pieces all the time, and have been pretty happy with it. My only complaint is that there's no ability to add comments, as with the 700. Bookmarks are often a good substitute.
A lot of people will tell you that .PDFs aren't the ideal file format for reading on a 6" screen, and they're right. However, there are a lot of tools available here at MobileRead for making them easier to read, e.g.:
PDFLRF
Rasterfarian
PDFread
SoPDF
PaperCrop
With one or more these, along with Acrobat, I've been able to get almost every published academic piece I've wanted to in fine shape for reading on my Reader (I use SoPDF and PDFLRF the most) even if the original file has stuff like tables and mathematical symbols that complicate things.
But overall journal articles aren't as tough as unpublished manuscripts or papers that peers or students send you. Professional type-setters know that you shouldn't make pages/lines of text too wide without putting in columns to break them up, but non-professionals don't, and then, a PDF becomes very difficult to get into the right shape. (However, then, you can often request the original word processor document instead, change the paper size, repaginate and convert.)