I am very pleased with Sony and this update. I was waiting to see what they would do with it; if they had abandoned the PRS-500 altogether, I wouldn't have bought any other Sony reader.
Now I am going to wait for the PRS-900. I suspect the trade-in offer will be extended to the PRS-900 once it is released ($50 for the PRS-300, $75 for the PRS-600, and $100 for the PRS-900. Isn't that a nice symmetry?

.) If I like the PRS-900's screen, I might go for the trade in. If not, I'll probably send my PRS-500 to be updated.