This is from Wikipedia...reliable enough for something like this;
"Although the service itself will be free of charge, content will be available on the PlayStation Store, such as clothes, furniture and game specific accessories, which can be purchased, but some might be available free of charge."
Fine by me. I'll stick with what they give us to begin with. The idea itself is brilliant, I think. I'll probably spend quite a lot of time messing around in there, chatting and listening to friends' music.