Anonymizing System Logs

My colleagues and I have obtained access to a large collection of  
system logs from 5 major supercomputers, and are currently working to  
get them into a form such that they are suitable for public release.  
These are raw logs, aggregated, in some cases, from many log- 
generating components (Lustre, netwatch, eventlogs, syslog...). They  
represent, cumulatively, more than 775 million processor-hours.

The primary pieces of data that we are trying to anonymize are  
usernames, group names, pathnames, and IP/hostnames. So, we are  
looking for some input from the log analysis community.

1) Aside from some possibly-excessive pattern matching, can you  
suggest a good way of masking out this data from the unstructured  
message bodies?

2) Assuming that all such data was successfully removed, what other  
security concerns would you have? How might we address them?

We would greatly appreciate your help.

Sincerely,

  - Adam J. Oliner
    [email protected]
    Department of Computer Science
    Stanford University