My prs-505 is great at what it does, so my next new toy would tend to need to be very different as far as features or form factor to get me to buy it. A notable exception would be if sony brought out a prs-510 that was a 505 with more memory, faster pageturns and the multilanguage support of their current devices so I could get english menus on a german model without having to reflash it like I did with my 505.
