I've been setting up quite a few WordPress-based sites in the past couple of weeks, and each time I install the FeedSmith plugin as a matter of course. This simple (yet brilliant) plugin was originally written by Steve Smith, and he eventually donated the plugin to FeedBurner and they adopted it as their official plugin.
As a result, the FeedSmith URL - http://www.feedburner.com/fb/a/help/wordpress_quickstart - became VERY highly ranked in Google. Type in FeedBurner FeedSmith and you'll see what I mean.
However, this old URL was changed permanently when Google completed the transition from the service's original feedburner.com domain to google.com. Bizarrely, for a company whose core offering is a search engine, nobody at FeedBurner remembered to check that the listed URL to the FeedSmith plugin was still valid. (It's not.) Bizarrely, even the plugin's original author's site still lists (as of July the 28th, 2009) the wrong URL!
I spent a fair while looking for FeedSmith, and then (after finding it once hosted by somebody else on their site) I stumbled across a poorly-linked mention of FeedSmith via Google's AdSense For Feeds blog. Can you see the link to the plugin on the blog?
No, neither could I at first. But after swearing blind that I'd seen a mention of a WordPress plugin, I did another scour through - and bam, there's the FeedSmith plugin link, nestled in an article called "Redirecting your feed to maximize revenue potential".
Clicking through to the Google Answers thread, I was almost put off the scent - the article's titled "Creating your WordPress Feed (self-hosted WordPress)", which has nothing to do with FeedSmith. However, the updated (and correct) direct link to the FeedBurner FeedSmith plugin is right at the top of the Installation instructions.
The functional direct link (as of July 2009) is http://feedburner.google.com/fb/static/feedburner_feedsmith_plugin_2.3.zip . I've had occasional problems with WordPress 2.8.x (so far, up to 2.8.2) being intermittently unable to automatically install the plugin from an upload of the zip file (apparently the file doesn't 'have any valid headers') - I think it could be because the plugin's nested in one too many folders. Either way, extracting the single .php file and uploading into wp-content/plugins works a treat. Just activate it in your Plugins section and add in the appropriate URLs, and you're done.
Suggestion to anybody from FeedBurner / Google if they're reading: add a 302 Redirect to the old URL! It shouldn't be too hard, you pretty much Own The Internet. You still own feedburner.com so this shouldn't be too hard (if you can't manage to sort it out on your own, my consultancy services are very reasonably-priced) - there's nothing worse than poor SEO, and forgetfulness is no excuse for disregarding the entire point of a Uniform Resource Location. I'm seriously disappointed in you. That's a Bad google. BAD Google.
Anyway, hopefully this will become a well-spidered article on all the search engines, and people will once again be able to find the correct URL and install the FeedSmith plugin on their own sites. (To the Internet: you can thank me later!)