Frankly, I'd only stick with Sony Library Software if you live in the USA. In Europe Calibre would be better.
Sony Library Software syncrhonizes perfectly with the PRS 900. One creates collections on the PC and then syncronizes to the PRS 900.
One must set up an Adobe ID and password first at
www.adobe.com. Then install the Sony Reader Software.
Then you can easily buy books at the Sony Reader Store from your PC with those purchases automatically syncing to the PRS 900.
Personally, I do most of my reading on the PC with Sony, Barnes&Noble and Amazon Kindle software. I use the PRS 900 for reading away from home. I am not sure if Calibre has as good a reader as the big three since I have never used it. I find purchased books are far batter than any free books but that is my personal opinion. The big three compete with big price differences and you can shop around as long as you will read them on the PC.
Your library may offer books free using Overdrive software but you must have a library card to read this way.
There have been problems having both PDF and ePub books on the PRS 900. Thus, I only have ePub books there. I read my PDF books on the PC only using Adobe Reader 9. If the PRS 900 ever freezes, just do a quick charge for 15 minutes and that will usually unfreeze it. If the freeze happened with a specific eBook, open to another eBook after the quick charge. Then start on page one of the frozen book and the freeze will be gone.
Keep permanent bookmarks and notes on the PC. Delete all bookmarks and notes on the PRS 900 after using it and transferring all that information to the PC. Extensive bookmarks and notes tend to freeze the PRS 900.