Microsoft supposedly spent 18 months working on the 45 built-in system sounds for Vista. This may seem like a long time (and I guess it is), but I have yet to use an OS where I enabled the system sounds for any significant amount of time. It may not seem like a difficult task to come up with 45 short sounds, but they need to appeal to a lot of people, produce a cognitive association with a specific type of event, sound good on a wide array of sound production devices, etc.
OS X has probably been the closest to acceptable to me. With previous Windows versions, I’ve usually turned off the system sounds within just a few days of turning them on. I’ve been trying out the standard set of system sounds with Fedora Core, but I’m not too enamored with them, either.
I was pretty surprised to learn that Robert Fripp was hired by the Vista team to produce a lot of recordings, some of which were used to develop the four-second startup sound. It turns out that Brian Eno actually did some recordings from Windows 95. I don’t remember any Windows 95 sounds being particularly Enoesque, but then I don’t remember Windows 95 very well at all, either.