The DX's screen and PDF capabilities (PDF handling could be improved of course) are beyond awesome. Didn't think I would ever use a book reader this much!
If you read anything with footnotes, the DX is a must. (otherwise you will be turning pages forever.) Also, with academic stuff I find I need to often glance back at a previous paragraph for reference and more text on a screen makes that a lot easier.
Since getting mine, I've certainly learned a lot more about PDF's (creating, formatting, reducing the size etc.!) - books are only part of what you can do with this bit of kit. It really shines with documents, reports, manuals etc. (wish it were easier to organize PDF's though) The size hasn't been an issue for me - interesting to see if this skews somewhat along gender lines? (in my case, I just toss it into my (padded!) backpack and head to the office or Starbucks. Fits perfectly and the cover (definitely buy or make a cover) offers a lot of protection. As mentioned, someone who uses a smaller backpack or a purse might have more problems. Similarly, the weight of the DX is fine for me and I can totally lose myself in a book with the best of them.
I thought reading in public with the DX (so far at Starbucks, on the bus or at a local Asian food court here in Seattle) would be clumsy or awkward, but has turned out to be a good experience. Again, the cover is great for holding and the unit is big enough, and type clear enough that you can still set it to one side and still eat and read. The experience has been a lot more discrete than I imagined (or dreaded
Good luck with whatever model you decide on - I know you will get a lot of enjoyment from either one! -J