I've started using Google Alerts to track usenet (Google Groups) posts on topics of interests, and all posts that contain a unique string I attach to my usenet posts as a "tag" . Alert search scope can be restricted to Groups, Blogs, Web, News and (shudder) Video.
Alerts appear in the form of emails however, and that's intensely annoying. I prefer to use email for communication, not as a general notification engine.
The cure is to provide Google Alerts a Bloglines' disposable feed reader integrated email address ...
...Bloglines free email accounts allow people to receive email newsletter subscriptions within their MyBloglines page. This helps to reduce traffic through your primary email inbox and helps to contain the spam menace. A Bloglines email account gives you a trump card when a newsletter breaks the rules of opt-in marketing. When you unsubscribe from a Bloglines email subscription, the email address disappears. You never have to worry about trying to find the unsubscribe instructions for an unwanted mailing list.
So the results of my alerts show up in my bloglines feed reader as event notifications, which is exactly what I want.
 I've done this since the launch of the original DejaNews in the 1990s. My usenet posts contain a unique string as a "tag" (keyword, meta term). I search on the string to find all related posts. The functional result is rather like a blog, but this method worked long before blogs existed.