Nmon can be run on the server to gather stats.
nmon also has a Excel spreadsheet to import the data and produce pretty graphs.
Sameer Verma also runs munin on the Jamaica servers to gather rolling stats.
Sameer’s student Ben Tran used munin in gathering data for his thesis on loading
the server. http://wiki.laptop.org/images/4/46/Testing_the_OLPC_School_Server_Benjamin_Tran_SFSU.pdf (see page 44)