An interesting article comparing a Dual 2.7ghz PowerMac Tiger Server
vs. Mac mini:

"The Mac mini is a credible performer as a limited use server. Why?
How? Mac OS X Tiger."

...."The server environment consists of log in accounts, email
accounts (POP and SMTP), Apache web server, MySQL database, and a
handful of PHP applications."

http://www.mac360.com/index.php/mac360/more/dual_27ghz_powermac_tiger_server_vs_mac_mini/

Paul