So you'd think, given that Portal requires Oracle Internet Directory (OID), there would be a nice easy way to capture user ID info in the Portal's Apache log files. I mean after all, there's the mod_osso running in Apache that is supposed to connect the Portal to the OID.
But you'd be wrong--according to Oracle support there's a bug that makes user ID logging unreliable at best. We're going to try and upgrade to the very latest patch of the Oracle HTTP Server (OHS, essentially a custom Apache config supported by Oracle). Oracle support says that may fix the problem, though they sounded doubtful.
This is apparently a known bug but they don't plan on fixing it until the 11g release of these technologies.