I converted all my PDFs to ePubs and reloaded the SD card with about 2,000 titles. I put it back into the 650 and let it load everything up. Other than a single auto-restart during loading, I haven't had any freezes or lockups since doing this. With no freezes, I've been able to put the reader through it's paces and I'm much, much happier with it now. I hope this, or the 600 thread I posted a link to previously will be of some help to someone else.