That's the beauty of blogs. Whenever you add a post, it tells the blogging world that there is a new post on your blog. So, when people search for blog posts about whatever you wrote about they may pick your's to visit.
Oh yeah, for anyone using my script from above, you might want to update it. Icerocket won't let you pull their feeds. So, I edited it above and changed it on my site.
And another thing, WP-Autoblog DOES work with WPMU! Rock on!