loading a lot of files from sd-card (e.g. epub, pdf) is a never ending story for PRS devices. once i loaded about 500 pdf (total about 500mb) onto sd-card using the sony library. after disconnecting the prs-505 it took hours until the refresh was complete. deleting a single pdf from the sd-card results in a complete rescan of the entire card...again several hours. The PRS-900 isn't better when it comes to files on sd-cards. Bottom line : do not use many files on externals cards, try to use internal memory only. i know this is a bad advice. Sony ads say you can have about 16.000 books with you. They didn't tell about scan and rescan times...