Feedburner feed takes hours to update; how to fix?

I use Feedburner for my RSS feed (mainly because several books I read said that was a good idea). While my native WP feed updates instantly, my Feedburner feed takes 2-3 hours before it shows a new post. I use Feedburner Feedsmith plugin to redirect the feed and Ultimate Plugins Smart Update Pinger to be sure a ping goes out when I post, and I’ve manually pinged Feedburner as well. None of this seems to have any affect — Feedburner still doesn’t update for 2-3 hours. Any suggestions on how to rectify this, or is this the way Feedburner actually (rather than is supposed to) works? Is there any reason why I shouldn’t just use the native WP feed, which is instantaneous? Thanks.