FeedBurner FeedSmith is the newest weapon in FeedBurner’s arsenal of weapons(no, not the destructive type).
Probably the most popular feed-related plugin for WordPress users, FeedSmith is just the old Feed Redirection Plugin by Steve Smith, rechristened and rebranded as FeedSmith. From now on, FeedSmith will be maintained and updated by FeedBurner.
Feed Redirection plugin works by some PHP stuff and user-agent detection, to redirect all feed requests to the FeedBurner feed. It can even redirect your existing subscribers. Amazing, eh?
You can set it up for both post feed and comment feed.
The current version can be used without hindrance, but in future, updates will be available directly from FeedBurner.
I’ll leave you with Steve’s explanation of how it works:
Using some WordPress plugin magic, and user-agent detection, this plugin simply forwards all your feed traffic to FeedBurner. The plugin will detect all ways to access your feed (e.g. http://www.yoursite.com/feed/ or http://www.yoursite.com/wp-rss2.php, etc.), and redirect them to your FeedBurner feed so you can track every possible subscriber. It will forward for your main posts feed, and optionally your main comments feed as well.