UPDATES AT BOTTOM OF THIS POST
Today Google started to merge Feedburner.com into the Google family. Part of this integration includes Adsense for Feeds, which include Google ads into your RSS feeds. I requested to be migrated today and after enabling the Adsense for Feeds in my control panel, all my Feedburner hosted feeds started reporting a 404 Not Found error.
As of this post, those feeds have been offline for about 8 hours. I am in contact with support at Google and have seen others report the same issue in this support discussion on the Feedburner Support Google Group.
If you were thinking on migrating, I would suggest you hold off until this issue is worked out. I would hate for others to suffer the same outage I have.
I will report more information when I have it.
August 16, 2008 - 1105pm PDT: In talking with Adsense Support, they asked if I was somehow blocking the new Google-based address for the program that accesses the source feeds for Feedburner. This doesn't bode well, as it could mean that there could be some issues between the new Google bot and GoDaddy hosting services. Feedburner reports a Error 502 - Bad Gateway when trying to access my feeds, regardless of what blogging software created them.
August 17, 2008 - 1043am PDT: Feeds appear to be working again. No word yet from Google regarding why the issue occurred, but I was working with them via email until 1am this morning. Somethings changed and that is a good, good thing.