How do I get a list of all the Alerts someone else is subscribed to?

You can view your own alerts through the Alert Plus Subscriber Web Part, but you cannot view the alerts to which others are subscribed. This functionality is available with Bamboo’s Alerts Administrator web part, Site Administrators can manage SharePoint alerts for sites across Site Collections within a Web Application. Administrators may create new user alerts, as well as view, edit, remove, group, filter and enable/disable existing SharePoint alerts.