There are more and more blogs and news sources appearing on the internet every day. It is becoming quite a challenge to filter out only the topics that interest you. RSS, Atom and similar feeds help a lot, but they are more site centric and not content centric. What I was searching for a few days ago was something like Google, where you enter a search string and then get the list of results. But I also wanted all these results to be delivered to me automatically, when they appear on the internet. And so I found PubSub.
PubSub is a free service that enables you to define some subscriptions (like searches in Google, but more advanced). PubSub then watches for all new content that gets created on sites in its database and if it finds a match for your subscription it immediately notifies you about that. Notification can be sent using e-mail, SMS and instant messaging protocol Jabber/XMPP for example. If you don't have a Jabber/XMPP client yet, they even offer a special sidebar extension for Mozilla Firefox that uses this standard IM protocol.
After using PubSub for a couple of days I can say it is working very well. If you need something like this I suggest you try it. It is free, so you have nothing to loose.