I chose the subject of my diploma: "The conception of file system in a virtual world". I will program a desktop that will display icons in three dimensions. There will be three coordinates - the third one will sort files by property that user can choose: filetype, size, category of users and maybe something else. It will look like layers - on the first layer we see mp3s, next one will display pdfs, etc. Changing of layers will be managed by mouse wheel - I think, it will be more usable but I'll think more.
In fact, I have no a clue how to do it so I'll have to read a lot of manuals. This summer will be interesting and it will be good experience.