One more from way down the cascade of comments of... variable quality:
I have concluded that the correct way, of thinking about OS’s is not as grand building designed and built for a purpose, with majestic skylines, but as city infrastructure, with streets and sewers, that should just work. However people will only notice your system when you overflow into the basement. A infrastructure that is not over taxed is in a city that is not growing, if your OS sucks because it is being taken places that won’t considered when it was first build, well there are worse fates.
-- Joe @ http://esr.ibiblio.org/?p=538#comment-228552