On VersionEye you can follow more than 335K open source libraries and as soon one of them release a new version you get a email notification. I follow more than 150 open source libraries and receive email notifications to stay up-to-date.
The notifications are available as RSS feed as well.
Some of our users are using the RSS feed heavily and they asked me if it would be possible to turn off the email notifications. It makes completely sense. I just pushed an update to production. Now you can turn on/off the email notifications in the settings.
Let me know what you think.