I use Radium to stream terrestrial stations and XM stations. I asked the developer to implement a pause, rewind, ff and go to live feature but so far that hasn't happened.
When I saw Intermission, I immediately jumped on it and bought it. It works exactly as you would expect. Basically its hijacking audio out and storing up to three hours of content.
There is one shortcoming you should be aware of. If you are listening to streaming radio and then use intermission to pause, then go start some other audio clip or music, you will not hear anything until you un-pause intermission. So all audio out is paused together, no allowing you to pick and choose which app's audio you want to pause is a minor negative but probably something we will have to live with. Selective app audio pausing is probably a whole other ball game.