One of the critiques of RSS feeds in a world dominated by Facebook and Twitter is that RSS just isn't fast enough. You can't hope to achieve what Twitter calls "in-the-moment updates" and "watch events unfold" if your client is polling each web site's RSS feed once an hour for new microblog posts.
Luckily this was solved years ago. Many blogging apps (including WordPress) have a setting to "ping" another server when a post has been published. When it receives this notification, the other server can request the RSS feed and make note of the new post right away.
Manon is right. This is actually a huge issue with the Open Microblog spec right now. I'm still trying to come up with a standard way of working around this issue (if you have suggestions, contact me).