Does anybody know how Feed aggregators like Feedburner, Technorati, etc check if the feed has been updated? There are feeds like digg.com which changes every minute and there are some feeds that hardly change over a month or so. Do they keep pinging all these feeds say after 5 - 10 minutes? If they do so, they will still miss a lot of stories posted on digg and would be an overkill for the feeds that change once a month. Or do they use third party pinging services like pingomatic to let them know what updated? I believe the topic belongs to this forum, as I couldn't find a better forum to post it at.