I just test drove a 2011 Prius and I also took the opportunity to test out its ability to play music over its USB interface. I pulled the usb stick with mp3s on it that I currently use in my aftermarket stereo and plugged it in. It failed to recognize the media. Even the salesman with the manual could not get it to play. So prior to buying one of these, I would like to know if this is a common problem. Is the system picky about mp3s being in subfolders or filesystem types or formatting?