It took me all of, um, about 5 page turns to get used to the Sony 505, and even less time to appreciate how easy it is to hold compared to the physical version of some of the pbooks I have on there!
As for what books are available, annoyingly not all of them, and even when some books in a series are available as ebooks, others may not be - it can be very frustrating! However, there are a lot of books around to buy or for free, so I'm not going to be running out of material any time soon!
Welcome