I came here looking for the same sort of info, but either the results I'm looking for aren't provided by lsof and fs_usage, or I'm misinterpreting them. I just had an event where AFP went deaf on my Xserve, although nothing was written to the log. I used Server Settings to cycle it off/on, and while it came back, it claimed that every file that was open on the server when it went deaf was in use by someone. I had to shut it down and boot it back up to get it to reset.
Would there have been a more direct way to ask it "what files do you believe someone has open right now?", and to say "no, that file is not really in use. Take it off your list"?