Sony's official Rolly blog has confirmed what we already thought: Rolly is in fact a digital audio player without a display. They also claim that it has only one button which controls the "play / stop" of audio and is "basically the only button you use." Although this picture shows what appears to be a cluster of three in addition to a glowing blue, elliptical button. Of course, as we've seen in the Walkman W910 phone, Sony offers other ways to control music without buttons. Namely, an accelerometer coupled with Sony's new Shake control software would allow you to flick the Rolly right or left to advance or jump-back tracks; shake it to shuffle-up the music. That would be particularly useful in Bluetooth-shy Japan where Rolly is being heavily marketed. Whatever the case, Rolly is surely more than just a DAP as we've seen in the video, but that's as much as Sony will own-up to for the time being.
Update: Well what do you know, digital lifestyles spoke to some "senior" Sony sources who consider Rolly a "music-focused Wii on wheels." Seems like an integrated accelerometer with Shake control might be in the cards, indeed.