OK, I've seen the Sony PRS 505.
My first impressions were:
-excellent display
-a bit heavier than I expected
-annoying flash on page flipping
I went into a darker room to check how the display would look. I can say that it behave like a paper book in those low lighting conditions.
The visual quality is great! I was expecting font shadows or ghosting, but this was not the case. I know this is the quality of eInk we are talking about, so this wouldn't necessarily be a plus for the Sony.
The body of the reader is compact, and it seems sturdy enough.
I tried zooming in an open book, but after 3 minutes I cancelled. My colleague told me that the indexing hadn't been made for that specific file. From what I read on the forums, this indexing is made automatically if I upload the books using Sony's book copy software, on the computer.
Overall I liked it. A lot.
I would have liked to sample a Cybook Gen3 as well.
Anyway, I'm ordering it tomorrow.

It will be a long wait, those 5 to 7 business days.
Thanks everyone for your help!