I might be missing the point here but why do people here keep so many books on their reader?
After all you are only likely to be reading one or two books at any one time. Personally I only ever read one, and then move onto the next.
So I keep all my books in the library on my PC, and a back-up USB disc, and copy the books I currently want to read to the reader as required.
Once I have read a few books I remove them from the reader and copy a few more across. I probably have no more than ten books on my 650 at any one time.
As such my reader is normally ready for use less than 30 seconds after being removed from my PC.