In Leopard, launchd has some options that can tailor your now-working LaunchAgents for specific circumstances. For example, if you want your LaunchAgent to run only when a user has logged in at the Aqua console — rather than SSH or other login sessions — you can use the “LimitLoadToSessionType” key:
<key>LimitLoadToSessionType</key>
<string>Aqua</string>
Note that to find events that have been limited in this way, you must use launchctl’s “-S” flag to specify the session type. Otherwise, launchctl won’t find jobs that are specified for a different kind of session than the current one, as per Levi Brown’s post.
I also found the “LimitLoadToHosts” and “LimitLoadFromHosts” keys when looking this topic up in the launchd.plist man page.
Thanks to James Bucanek for mentioning this on the launchd-dev list.