Thom has already demonstrated the basic functionality and showed you how the personalized UI can look like, see his blog posts
here and
here. As for UI personalization, I will focus on differences between the version 4.1 and 5.0. I also feel responsibility to tell you what happen with some of the UI-related module permissions after you import your site package from older version to version 5.0 or after you upgrade your version 4.1 to 5.0.