I???ve done it twice (though only one of those is a web app), and in both instances, what I found was a need to be able to muck around with the lowest-level code to be able to create app-specific speedups???whether that was writing my own hand-tuned demented-but-fast SQL or being able to back stuff up against memcache that most people wouldn???t think to put in there, like mutexes (and yes, I know