bill - 1:12 am on May 6, 2010 (gmt 0)
Welcome to WebmasterWorld jordana.
I'm not a WP user, but many (most?) blog and CMS systems will offer you a means to ping RSS tracking services each time you add new content. However, even if you didn't use that feature, and you had manually submitted your feed to one of these services, like Yahoo, then they will eventually come back to check your feed for new entries. They have their own schedule for re-checking feeds.