A firmware upgrade for the PRS500 would be WONDERFUL! My wife and I own two, and have been mulling over the question of when to upgrade, and what device to upgrade to.
Lack of an upgrade for the PRS500 was causing Sony to DROP PRECIPITOUSLY on our buying list; bringing out such an upgrade would put Sony's next reader (after the 505, that is) back at the top of the list. We'd feel more comfortable buying from Sony if we felt that older models are likely to be well supported. It matters to us because we are "upgrade every-other or even every-third model" folks.