Today we’ve turned on PuSH support for the more than 10.5 million blogs on WordPress.com. There’s nothing to configure, it’s working right now behind the scenes to help others keep up to date with your posts.
PuSH is a way for services that subscribe to updates from your blog (think Google Reader, Bloglines or Netvibes) to get updates even faster. In a nutshell, instead of having to periodically ask your blog if there are any updates they can now register to automatically receive updates each time you publish new content. In most cases these updates are sent out with in a second or two of when you hit the publish button.
The only notifications you need are those sent directly to search engines. Since search engines also keep a close eye on services like Twitter it helps to send the content to them as well (feedburner has an auto twitter snippet posting service for wordpress).
I like to use the other services as intended, like Google reader, by letting them know I exist and letting them visit when they see fit. If every blog out there pings everything it possibly can a huge amount of noise is created that gets ignored because search crawlers are already working their own schedules.