Monitor Your AirPort
A colleague just pointed me to AirPort Monitor Utility, which allows you to pull statistics and other information from snow (but not graphite), and Extreme base stations. For instance, you can see how many users (and their MAC addresses) are connected to your base station.
It requires Mac OS X 10.3, and the best results are obtained from Extreme units which have more support for SNMP (Simple Network Management Protocol) statistics and reporting. The snow unit can't report on DHCP and wireless connections. The cost is $10 after a 30-day trial period. An improved 1.1 version is expected soon, according to email from the developer.