On a server with a lot of users, the log file can get very big. It's possible to archive the log.nsf file, but it doesn't reduce the file-size, and it's most of the time impossible to compact the log.nsf while the server is running.
The solution as proposed by ...
Enable email log output to be sent to a remote syslog host. This is especially interesting in mixed environments, where different messaging systems interact over SMTP.
I don't know about the rest of you, but I find Activity Logging and Activity Trends to be a really useful feature. Unfortunately, since it was introduced in 6 (or was it 6.5?) there have been very little updates to it, other than making the Tivoli Analyzer free in 7....