It turns out to be impossible to produce a legal, subscription-funded music podcast for worldwide distribution.
Like making a compilation album, I suppose, you have to clear the rights for each track with everyone involved, and this includes the master/mechanical/performance rights (you're not only copying a file, but performing it in public, says the law). The artists or record labels own one set of rights, while the songwriters or publishers own another.
You can get a blanket license in some parts of the world from licensing agencies for streaming audio, but this doesn't cover podcasts (downloadable, not streamed, so you can listen to any part of it at will, therefore has to be more expensive, say the owners) and even then that doesn't spread outside national boundaries. Is it the country the owner lives in, or the country that hosts the streaming server, or the country of the listener, or the location of the company that produces the stream? The latter, apparently, for streaming, but not necessarily for distribution.
Recently the Copyright Royalty Board in the US decided to increase the rates for online streams, more than doubling the per-listen cost over 5 years and removing the 'percentage of revenue' cost for small webcasters. It seems that this might take a lot of streaming audio offline, as people can't afford to broadcast, and there are suggestions that this might not be unintentional.
The prices at download stores are too expensive, at around $1/£1/€1. Their catalogues are crippled by licensing disputes and their DRM prevents customers from listening to the music they pay for, so they don't buy it at all. Rhapsody seems to have a great setup, with subscription-based payments, clients for all platforms and impressive third-party front-ends (see YottaMusic and MusicMobs) built on the web services, but is completely unavailable outside the US.
So we use music torrent community sites, which have extensive catalogues, early availablity, reviews and personal descriptions, social interaction and incentives for participation, but they're never going to be legal (at least not in a pay-per-download model) because this model just can't work in a system where the price of bandwidth is minimal compared to the cost of licensing, so any possible reward for uploading is never enough of an incentive to keep seeding torrents.
MP3 blogs and The Hype Machine do a great job of recommending and writing about music, and Songbird provides a great interface, but hardly anyone's actually allowed to post any of the audio files that this is built on. Last.fm is doing a fantastic job of providing every feature anyone could want for a social music discovery site, but until the licensing opens up and people can actually hear as much music as they could possibly desire, music delivery is just going to have to stay underground. Unfortunately this means no-one can charge subscriptions and make money out of it, so there's nothing to pay the record labels, songwriters, publishers and artists.