Just the 25K and, like ardeegee, use PRS+ nest by genre, by alphabet, sub-alphabet and author... works like a charm and not many key presses/taps to get to book and can now read direct off unscanned memory card rather than having to load into internal memory.
With PRS+ you can switch off auto-scan of card which is the big block to large numbers of books on memory cards or in internal memory... I regard my Sonys more as a portable library now and I never have to choose what I want to read in advance because everything's with me... just need another lifetime or two to read 'em all...
