I'm using this component along with EventList to send announcements about new events to users.
I have some issues with setup using Firefox 4, but with production browsers the component and plugin work fine.
There were some initial issues with the cron job but that is also working fine now (version 2.01).
If you use Eventlist, this is a great addition. You can also create a Joomla menu item for users to edit their subscription preferences, using the standard Joomla menu tools.
The component has many other plugins too - for Kunena Forum (latest posts etc), Phoca Gallery, Community Builder...
Now that 2.01 is out this is highly recommended.