Most important point: any log message that doesn't identify some property of the request that originated it (so that you can identify requests leading to erroneous conditions) is cause for immediate defenestration.
Agreed. We use mod_unique to add a header to each response and make sure it's included in each error log, back end access log and front end access log as well as being viewable via Charles/fiddler at the client. Being able to tie the various logs from different machines together has been invaluable.
