On WoWInterface (I don't know about Curse, but I'm sure it's something similar, same with wowui.incgamers), when you go to the download page of an AddOn you use and like, you can click on the little heart underneath the big download button. That adds it to your favourites list. Now every time you visit the site, you will see a notice on the front page (Community tab) saying whether any of your favourites have been updated. As well, there is a link on the top bar of the site that says "favourites", that you can click at any time to go look at your list.
To get email notifications of updates of your favourites, do this:
If you are on your Favourites list page you will see a little menu on the left, or if you are on any other page on the site (except the forums tab) you can click on "Options" on the top bar. Either one of those places you will see:
Click on "Preferences". You will then see this:
My Favorites Options
Enable this feature to recive email notification when one of your favorites has been updated.
Just check "yes" and any time any AddOn on your favourites list is updated, it will send out an email notification that it has been updated and give you a direct link to the download page for that AddOn.