As one of the people working on this project my view is highly biased, of course, but maybe I can tell you about my motivations:
I started using BeOS because I read how fast and cool it was. I installed it, was blasted away, and started coding for that platform.
Compared to my Windows and Linux installs, the responsiveness of BeOS was really incredible (today computers got faster and it’s not such a big difference). Another point for me was that I could finally understand everything about the OS from an end-user perspective. It basically mapped my personal understanding of an OS directly to the user experience. In Windows you have the bloated registry and in Linux you have hundreds of configuration files and scripts which, at that time, I often had to edit manually. It was just too much to learn and know, for no good reason. In BeOS you feel like you’re directly in contact with the lower level and at the same time things seem to be relatively easy (well, not perfect, but we’ll work on it). Also, BeOS offers this cool “I move this file here and it just works!” experience, for example, when installing drivers or add-ons. While on other platforms you really need an installer or special helper apps to handle the complexity, BeOS often makes things so simple that you could do it by hand.
What also really made me happy was that BeOS didn’t have totally overloaded configuration dialogs or 1000s of functions. It was kept simple. You don’t have to fiddle. You don’t get annoying system notifications. Plug-n-play is dead easy. Everything just works without getting in your way and you still have all the power where it really matters.
Regarding server vs desktop: I think the point is that our target audience is the home and business user. The desktop must be very easy to use and understand and everything must be more automated. On the server, only few people interact with the system directly and those who do are experts, so usability is not critical for a good app (it’s sufficient if it’s “just” stable and secure).
Don’t get me wrong. BeOS is far from perfect. Not even very good. Under the hood it’s slow and not very stable. There is no security. We lack important features. Also, I think there is much room for usability improvements. Fortunately, Haiku can fix this.
Our future:
We’re all here to build something new. R1 is just the foundation. Things will stay simple, but we want to introduce better ways of interacting with your computer and we will try to reduce complexity such that you can understand the system much more easily and at the same time get a more powerful platform. How much of this can be done will have to be seen (we’re secretly working out evil plans ;), but we will try to create a platform that makes you more productive and at the same time is very easy to use and not overloaded.
Uhm, I hope I didn’t promise too much. 
Bye,
Waldemar Kornewald