I've actually played with it today, and I have mixed feeling. Ended up reading things in landscape mode, with quick drop-in to zoom-in mode for any detailed images/graphs. Not ideal, but far better compared to what 505 can offer.
Now the question of course is whether I'd be happier with giant Kindle DX - I don't think anyone else is making >6" ebook readers. I'm kind of convinced that 650 would be the right move, as the ratio of technical stuff I read on the reader to prose is 1:3... but that might be just shiny gadget talk
Thanks for the opinion.