I think that it's important to understand that as a podcaster your feed stats don't mean much. I don't think there's a poll out there yet that shows more than 50% of any podcast's listeners actually use a podcatcher at all. In fact, many polls and surveys have shown numbers as low as 25% of listeners make use of a feed at all. Far and away, most listeners are direct downloading their shows.
So the real question is "how many listeners do I have" and not "how many subscribers do I have". Despite the best of intentions, it's become irrelevant how your listeners get your show.
What we've used on The JaK Attack! since day one is Awstats with a little modification to the configuration file. Awstats is a free (as in both meanings) stats package that's pretty easy to install and provides some really pretty stats. Out of the box, however, it doesn't present audio file downloads in a very meaningful way. Thankfully, the Awstats authors have included an 'Extra Sections' functionality which allows us end users to tell Awstats to track pretty much anything that we'd like.
Quite a while ago I wrote a post on New Linux User about how to add an Extra Section into an Awstats conf file to produce nice stats on MP3 and OGG file downloads.
The reason why this is such a great way to track downloads is because the only really accurate way to track downloads is to take the total amount of bandiwdth that a given file has consumed and divide that number by the file size. It's not perfect because there are probably some partial downloads in there, but it's about 40 bajillion times more accurate than anything else anyone else on the planet has come up with. It's brilliant in its simplicity because it has nothing to do with feeds or subscribers - just downloads regardless of how they occurred.
My entry on Awstats can be found here if you're interested.