This post has nothing in particular to do with libraries, but as the problem I relate consumed a good part of my weekend and part of my Monday, I thought a share was in order, in case anybody else runs into a similar situation.
We use Hipcast  for our podcasts here at Infopeople. We chose Hipcast (it was called Audioblog way back then - all of a year ago) because they offered great storage, and the ability to "phone in" your podcasts - a nice way around the problem of getting our podcasters remotely up to speed with microphones, software, etc. Sounds good. And it was - it all worked as advertised. They also offered very easy ways to publish your podcasts straight to iTunes and your blog. Slick! They even offered a nifty embedded player bar that would play the podcast right from the blog entry.
Then a strange thing started happening: our Infoblog feed would periodically disappear from My Yahoo. Hmm. It happened whenever we posted an entry about a podcast that had the embedded player in it (I didn't make that connection right away - it would have saved me a lot of time if I had). I tried validating our feed at Feed Validator  and got errors - and all of the errors pointed to that nifty little embedded player that Hipcast published to the blog. Turns out that nifty code (iframe src) that makes the player bar appear in the blog is considered vulnerable-to-hackers by My Yahoo, so a feed containing those tags won't show up. Argh!! The solution I came up with was to take out the player bar code and just put in a regular link to the podcast's MP3 file. Not as slick as the embedded player, but it works. My Yahoo RSS (as far as I can tell) is the only service affected by this weirdness.