I'm wondering how you all monitor bandwidth per machine (dedicated servers). I was going to write a perl script to use ipacct and ipfw but then thought mrtg would probably be a more accurate choise. Was wondering how you did it.

My personal favorite is to do both: Use a perl script to parse `/sbin/ipfw show`and pass the value into MRTG. It gives you all the information conveyed by MRTG, without the irritation of SNMP, and allows you to graph different traffic types (eg HTTP/Other TCP/UDP/ICMP) separately.

Of course, this relies upon your being able to trust the machine; it isn't clear if you want to monitor your own bandwidth usage or if you're leasing dedicated servers and want to monitor your customers. If the latter, then of course you'll have to get the data out of your switch or firewall.

As cpervia suggested your best bet is to use a switch that is SNMP aware, and monitor each port on the switch, that should give you the most accurate data.