If you have Rdio (and a Mac), you'll wanna download their new desktop app, which takes all the browser-based features of the streaming music service and gives it an iTunes-style UI and a home on your dock.
You can't download tracks for offline listening or merge your local MP3 library with your streaming collection, but it will manage any MP3s you purchase and download via Rdio. And from the looks of it, the app loads the same web content you'd find on their site, but now you can use the media playback keys on your keyboard to control playback and you don't have to go tab hunting in your browser to find Rdio. You can download it here. [Rdio]