You may already use one of several different Dashboard widgets for listening to BBC radio programmes over the net; but the team at BBC Labs has just released a new one that offers something a bit different.
It's part of a wider project called Radio Pop that turns radio listening into a social activity. As long as you're listening to your BBC programmes via the Radio Pop player (available in-browser or, as I said at the start, as a widget), you can "Pop" your favourites - in other words, flag them.
Your Radio Pop profile page shows what you've been listening to. Your Pops show the things you liked most, and give you quick access to programme information pages. Right now it's limited to live radio streams, but plans are underway to add the BBC's Listen Again output as well, which will make it much more interesting. (Developers: there's an API for you to play with, too.)
Since I'm in the UK, I haven't been able to confirm that this works elsewhere; YMMV. One additional requirement for making it work is a copy of Real Player, which the BBC uses for all its radio streams. Download it via the links on this BBC help page and you'll get a version that doesn't come laden with ads.