Hi Bob,
The iLiad does use a Vizplex screen, although they don't mention it in their advertising. That's because they already used a much better screen than the "1st generation" eInk screen that Sony used previously, and changing to VizPlex has made very little difference to the screen quality, whereas for the Sony it made a huge difference.
The iLiad is undoubtedly the best device for PDFs, but is it worth double the cost of the Sony? That's a tough call to make, especially since, as you rightly say, the Sony now supports PDF reflow, and that makes things a lot better for "text" PDFs, but won't really have that much impact on complex graphical PDFs, such as textbooks often seem to use (I'm not sure how good GVE would look
).
The way I think I'd look at it is that the iLiad is the one to go for if reading PDFs is your #1 priority, with fiction of secondary importance, and vice versa for the Sony.
Unfortunately seeing eInk devices in the UK is a bit of a problem at present. Some branches of Borders have the iLiad (presumably that's where you can see it in Cambridge?) but that's pretty much it.
See you on FC