If you have a linux based router such as a Linksys. You can load third party firmware that allows you to meter at the router. All applications I have seen have to run on each client.
Metering at the router covers your usage from iPhones, video gaming systems etc as well as the Macs.
Its criminal (or close to it) that an ISP that limits you does not provide an easy to reach web based meter of your usage.