I never used a memory stick - because the internal storage is far big enough!
As for the Iliad: i also was not that sure which one to take, but then i realised, that all i want it for, is reading. I don't need wlan, I don't need a touch screen, and for size reasons, the Sony reader is much better to carry around!
(I read on it on a train or outside, but most of the time at home)
=> So the Sony reader is the cheaper and (for me) the perfect reader!
As for security: I already dropped my precious reader
(about 1.5 feet), but luckily nothing happend! - And the surface is really perfectly constructed, i can see no scratches on it (after 3 month of almost daily use...)
=> And this is for the hole reader: It is on a very high build- quality- level!
greetings from Switzerland
_darius