Just as we have Data.gov to provide a single point of discovery for all government data, we should have an "Alerts.gov" that catalogs all the thousands of alerting and subscription services provided by the government. Today, it is simply too hard to troll through all the government web sites to discover what might be available.
Ideally, Alerts.gov would also allow a user to have a single shared interface for viewing or modifying all existing subscriptions as well as for creating new ones.
Clearly, it would also make sense to encourage technology platform consolidation among the various publishers of alerts, subscription services, etc. Doing this would not only reduce costs and increase ease of use for users, it would also allow sharing of new capabilities between publishers. (i.e. There are many delivery mechanisms beyond email, yet not all agencies can afford to build for them all. If there was a common platform, all agencies would have access to enhancements created for any one of them.)