>>4
OS development is a major undertaking, it's not the sort of thing you can do in a weekend, especially considering it requires low-level programming techniques that are avoided in modern application development. The appeal of things like Linux and BSD is that the hard work is already done for you, but unlike Windows or Apple operating systems you have the freedom to modify the user interface (which is all most people really care about, messing around "under the hood" is really only called for when working with embedded systems or mainframes, where you need to get every last bit of performance out of the machine - and only low level programming specialists really have the ability to effectively optimize in those areas, anyway). And the UNIX architecture, although rather old, wasn't really made for "mainframes", one of its main advantages at the time was that it could run on lower-end systems.