My 2009 iMac has been running 24/7 since I got it. During the day it is my workstation, and the other functions it provides is a group web server, and group backup server.
My Mac mini has been running 24/7 since I got it, and it is my home server for backing up my systems at home.
Adding to the mix, my G4's been running 24/7 since 2001 and the iMac since April 2010, except for the few occasion when on travel or when restarting due to installing software. I only sleep their displays, not the computers or HDs.