This must exist somewhere. I just can't find it.

I listen to a lot of podcasts in a week and I use quite a few different computers. One desktop at home, one laptop while out and about and a PC and an iMac at work. I want some service (or combination of web service and application) that I can use to manage my podcast subscriptions regarless of where I am.

At the moment, I have iTunes installed on my desktop, my laptop and the iMac at work and I have subscribed to my collection of podcasts in each of them. I want to be able to plug in my iPod and have it delete the podcasts I've listened to and get the latest episodes of each of my subscriptions. At the moment, I plug it into the desktop, copy on the latest 'Planet Money' and listen. A couple of days later, there's another episode released so I plug into my laptop and it offers the episode I've just finished listening to and the new one. A few days later, I'm working on the office iMac and plug in my iPod, it suggests the last weeks-worth of episodes. I have to manually go into every subscription and drag over the individual files that I want to listen to.

What I'd like to have is a web site where I can put in my podcast subscriptions and it will track the latest episodes of each. I can then either point iTunes to this site so that I can point all my installations at it or it will provide an application which can be used to put the latest episodes onto my iPod. When I plug in my iPod, the application tells the site which ones I've listened to and it removes them from my listening queue. The application could, also be stored on the iPod itself to enable it to be used wherever the iPod is plugged in, not just on computers with iTunes.

Am I explaining myself clearly enough? It just seems so simple, it should already exists within iTunes. It is entirely possible that Apple's recent acquisition of Lala could be the first step in an online iTunes which would solve these problems. If anyone has any suggestions for the best way to achieve this, please let me know. I thought of a way of doing it with Dropbox but it would only work if the music bit of my iTunes library weren't bigger than my Dropbox account.