BeOS's focus was and still is to create an OS that trades off throughput for latency on several levels (desktop and multimedia holy grails).
BeOS was a very slow OS, but it felt very responsive.
I think it died in part because of the direction Be took (the Be Box, etc.) and in part because they tried to compete with Microsoft on their turf, people would see the OS demoed and be very impressed untill they heard there was no Outlook, nor any MS Office. However I hope Linux one day will be able to give us similar responsive computing.