Google Reader now publishes feeds in real time. This means posts appear in Google Reader as soon as they go live on a site. These real-time updates will however only work for PubSubHubbub-enabled blogs.
Every blog on Blogger and Posterous supports PubSubHubbub. If you want to enable PubSubHubbub on a WordPress blog you need to install the PubSubHubbub plugin.
If you use Feedburner to publish your RSS feeds, you can turn on Google’s PingShot service and sent out PubSubHubbub announcements in real time.