If you're reading LRF files on your reader, the Sony software will "pre-paginate" the files when sending them to your reader. This will allow the files to open much quicker, and changes font sizes for the first time will also be much quicker.
This doesn't apply to ePub files. They'll load just as quickly no matter how you transfer them to your reader.
And FYI--the files you copy to the reader don't necessarily need to be in any specific folder. The reader will find "readable" files no matter where they're located.
Hope you enjoy your new 300 as much as I enjoy my 505!!
dordale