I have a social networking site which is beginning to gain some momentum and has an expanding user-base. We currently allow the users to import their blog, flickr and twitter feeds. We use the php library simplepie to read the feeds and then we check the DB to make sure we do not have a duplicate entry for each found feed item. If the feed item is new, we store it in the DB. The feed updaters each run on their own cron. So we have one for twitter feeds, one for flickr and one for blogs.
I have noticed the site gets sluggish and it is most likely when the cron tasks are running. There must be a better way to do this. Any thoughts?