My findings on the $40, $50 and $60 LTE plans through Metro Pcs.
After searching the internet hi and low for what exactly Metro Pcs considered "multimedia streaming access", I think I have the answer. From my experience, after switching to the $50 plan, any video, watched on an app or even via web browser, has counted toward my data usage. Audio streaming, downloads from the Market, and web surfing, through web and 3rd party apps, have not affected my usage.
Sorry if this has already been covered in another forum, but if it has I sure couldn't find it. Just wanted to pass my findings along.