Looking for a quick win? Try correlating your 404 pages with your servers report. On larger sites, multiple servers are used to deliver the pages with some kind of load balancing. The problem that can come of this is when there is a code push, errors can occur and the push does not make it out to all of the servers and errors ensue. By being able to break down your 404 error pages by the server that is deloivering them can help spot troublesome machines, or code pushes that didn’t quite make it out to every machine.
Not using the s.server variable yet? Get on it!