Radiotagbot is a way to bookmark the current point in a programme that you're listening to (or watching) live, by using twitter. To create a bookmark, you send a message to @radiotagbot with the name of a BBC radio or TV station in in it (e.g. "radio 4" or "r1x" or "BBC1") and it will tweet back to you with the title of the programme and a link to the point in time on iPlayer at which it will (usually) appear. If it's on Radio 1, 1x, 2, 3 or 6 Music, it will also attempt to reply with the music track playing.
Via Nicolas Weil