Happened to me today
I started having problems on my laptop today. I have the hard drive partitioned into two volumes (one for everything from Apple, one for my own stuff). With 65 open tabs/windows in Safari and oodles of other stuff, I was low on VM (12 swap files). I started getting alerts about being low on space on the startup volume. Disk Inventory X revealed that /var/log/windowserver_last.log was 6GB! The entries were all error messages from today.
I created /etc/daily.local, copied the log-rolling code from /etc/daily to it and changed the log files to windowserver.log and windowserver_last.log and ran it as a test. It worked terrifically.
I'm not sure this log rolling is needed, since none of the other machines have large /var/log/windowserver* files. But I figure it won't hurt.