The Blogroll Update checks pingomatic.com (every 15 minutes) and weblogs.com (every 5 minutes, using the shortChanges.xml feed). If a link from your
Not really, but it's helpful if you'd like to see which links on your blogroll have recently updated when used with the get_links template tag or a plugin that displays your blogroll, like my Blogroll-Favicons plugin (http://www.hitormiss.org/projects/blogroll-update).
This plug-in combines what each of those files does (checking weblogs.com and pingomatic.com). Right now more people are pinging weblogs.com, but over time they will hopefully shift to pingomatic.com. Also, this plugin checks the two services on a regular basis without having to use an external file or a cron job.