In response to my post - feedburner invalid feeds, I received a request for samples from Eric(Feedburner) which I quickly sent out and this is what I got back from him:

You're right, the feed is invalid because of some bad character in one of the posts. The invalid character is in the source feed, however, and it's making it so even we
can't parse the feed. So what we do when we can't read the feed is that
we a) automatically notify the publisher that their source feed has
become invalid and b) pass the feed through as-is without applying any
services to it. So, what you're seeing the the original feed without
things like the "Browser Friendly" service applied.

When a publisher is setting up their feed with FeedBurner initially, we
don't allow them to burn an invalid feed ... but feeds can become
invalid over time, as you've discovered. So, an interesting debate to be
had is: when a feed becomes invalid, should we allow it to pass through
FeedBurner, or should we instead return the "last known good" version of
the feed until it's fixed? We've gone back and forth on that issue, and
we've decided that it's probably in the publisher's best interest to
just notify them and to let the invalid feed pass through. That's at
least a bit more visible to both the publisher and subscribers --
otherwise, it would just look like the feed was frozen.

What an interesting response for an interesting topic - How do we publishers post valid content so that our feeds do not blow. I do understand Eric's point of view, they can only do so much. You can't really force a horse to drink, they have helped us with tools for our feeds, its up to us (publishers) to provide valid content for those feeds.

Do we need to create another standard for the content of rss feeds? I don't think so! but we can definitely provide some kind lines for proper feed content such as:

   Rule #1: Use a reputable blogging tool with valid text editors

   Rule #2: Try not to use invalid characters

   Rule #3: Validate your feed on a regular basis (I need to do the same :( )

   Rule #4: Blogging web applications need to implement rss validators internally on publisher posts such as feedvalidator.org