Because most of the documentation for this is in my head:
Some machines are in active use. See Machines.
Many hide in the InterfaceCupboard.
You may also be interested in HowSwansWorks
And they do some network traffic: http://interface.org.nz/~don/rrd/external.cgi
And a list of changes made to systems, by SysAdmins: /ChangeLog
Also /WishList