One thought that immediately came to mind. As much as Beryl has an unbelievable cool factor. I am not sure it leverages any real increase in lateral visual adjacency. Lateral adjacency to me is the primary limiting factor for user interfaces at a practical level. By definition showing items at an angle lets you see more items in perspective. A rotating cube on the other hand at most shows you three options.
Also see the comments on this life hacker post on dual monitors.
And researching links for this post I just found UltraMon. Wow! Definitely going to test that one out!