Hi, this message is meant for anyone who has the power to insert permanent changes into the official WordPress codebase.
There is a fairly common bug with WordPress's RSS/Atom feeds. It doesn't happen to everyone, but when it does occur, wordpresses various feed xml documents end up with some extra blank lines at the beginning. Since the feeds are validated XML documents, these extra blank lines are not allowed, and will cause many feed readers to refuse to parse the feed, with an error message like: "XML or text declaration not at start of entity."
If you do a google search for this problem, you'll see that quite a few people are encountering it.
The root cause of the problem is plugin developers that leave stray newlines at the beginning or end of their .php markup tags in their php files. Someone even wrote a plugin that strips all the leading and trailing newlines from your wordpress .php files, and even that doesn't always work (it didn't for me)!
This is a very frustrating problem for those of us who experience it, but happily there is an easy fix that will solve the matter for everyone. AND we don't have to rely on forcing every plugin and wp developer to be really disciplined about their stray newlines.
There is one solution near the end of this forum posting, involving ob_clean(): http://wordpress.org/support/topic/156727?replies=63
And there is another solution (it's one I tried, and it works perfectly) here: http://www.w3it.org/blog/wordpress-feed-error-output-solution-how-to/
Both solutions involve a last-minute removal of any stray newlines that have been added to the beginning of the feed xml documents (regardless of how they got there). As far as I can see, there's no downside to adding a couple extra lines of code to do this at the beginning of each *-feed.php file, and it should pretty much squash this bug cold.
That second link that I provided gives the exact details on how to patch the WordPress codebase. I take no credit for thinking up this fix, but I would very much like to bring it to the attention of the WordPress dev team. It seems like a very easy, low-risk fix to a problem that will otherwise keep coming up again and again.
Please consider adding this in there, guys. Thanks!