Custom logging for web applications
rarrrrrr: A few months ago we actually created a system that does exactly this, plugging into the Ganglia data visualization system many sites use.  We have bindings for Perl and Python.  Your app code just emits non-blocking UDP packets to a local collector daemon and goes on with its business.
GPLv3 code here:  https://spideroak.com/code  (StatGrabber)"If you can't measure it, you can't manage it."It's really nice to see graphs of the business or application specific stuff (signups, connected users, revenue, anything that's event driven) in parallel with the regular system graphs of things like bandwidth, memory, and so on.  When you look at the weekly or monthly graphs usage trends and bottlenecks become forehead-smacking obvious.Ganglia demo: http://monitor.millennium.berkeley.edu/