Podcast subs is actually one area that works pretty well across platforms and operating systems, thanks to OPML. iTunes does let you import and export OPML and many other clients support it in both directions too. I think Google Listen, which is now deprecated, did let you do this too via Reader.

The part they all fail on (which I’m aiming to rectify) is cloudiness; they almost all require you to export from one programme to your drive and re-import again to another. And don’t even think about making your subscriptions public when they don’t even live in the cloud. It’s archaic, but a small annoyance compared to other forms of media.