Let's make one point here ... there is no difference (here) between MP3 and AAC. POM runs a conversion on AAC that sees to that.
And another point ... you can feed iTunes with no more than just your show posted on POM. No need for Blogger or Feedburner.
It is interesting that some are getting locked up while others are not. As has been pointed out, it all leaves the server the same way over the same pipe. Some Microsoft software - WMP 9(?) - is problematic while others - WMP 11(?) - is not. Safari (Mac) with QuickTime (Mac) works fine. You may want to find out what your listeners are using, but I wouldn't be at all surprised to hear that they don't know! Maybe they know which browser they are using, as likely they don't even recognize IE (what's that?) or iTunes are browsers and that they use plugins (WMP x and QuickTime) to actually play files. In other words ... "good luck". But, this may be the only way to clear the problem up. Who knows ... it may be your listeners who are still using Win '95, or the ones who've upgraded to Vista who are seeing the problem.
Dave M

I'd also appreciate an update. Being Pro doesn't seem to get the attention promised - I've emailed support three times about this over the past week and not yet received a reply.