PubSub is a tool to push feed items to your desktop. You register at PubSub, identify topics of interest and the news will start coming to your desktop automated and in near real-time.

This model shares the same weakness as email. Both push content to your desktop. Email now also pushes spam (around 80% of email is spam as per NYT) to your desktop without your consent. The problem with push model is that it is easy to exploit it and feed spam. Anyone can submit feed to PubSub and it is easy to create and submit hundreds of spam feeds to PubSub to easily pollute the results. In fact they can be easily automated by any programmer.

However a simple pull model where you subscribe to feeds of interest like New York Times or Wired News etc. are much less likely to go wrong. You can choose the quality feeds and then use an online (BlogLines) or offline aggregator to view them.

Update: It appears I was correct. PubSub site went offline as of 15 January 2007 due to financial trouble.
BTW: Pubsub's assets were bought by another company which plans to re-launch the site but that is another story.