WordPress made the recommendation to upgrade to version 2.0.6 due to the new security fixes it offered. However, this new version has a little bug that is playing a little havoc with Feedburner Feeds. The bug is not security related, it only has a possible effect on some RSS readers and some servers.
Mark Jaquith has a post that explains everything and tells you what to do about it.
Since I just posted yesterday about the WordPress vulnerability, I thought it was important to get the word out about this little glitch as well.
Shout out to Quick Online Tips for mentioning this too!