According to its creators, the new operating system BeOS is a "Media OS". This is because they say they designed it from the ground up to perform for users and developers in this 'multimedia" age and the future. Idealogy is nice, but what they've got may well be better. Pick a buzz word (Protected memory? Multiprocessor?) and you'll find it in the system architecture. This OS was designed from the ground up over the last decade. It is truly a new, next-generation OS. This paragraph can not begin to do it justice.
For more info about Be and their BeOS, see their site at http://www.be.com or their guided tour at http://www.be.com/products/beos_tour/index.html
The UI is discussed directly, with screenshots in BeOSUi