I am finding with some larger MP3s (5Mbyte) that the player just sits there with a "buffering..." message, and does not play the audio. The MP3 link still works fine and plays almost immediately through an external media player. Checking network access through Firebug, the MP3 does download fully and quickly, so I am guessing the Flash is not handling it properly.
And those bright red contribution nags that appear all over the place - they are am embarrassment. Please remove them. If you don't, you will find your plugin forked or copied, and then you will lose a lot more. That's not a threat; it is just an inevitable way that people work around annoyances on the Internet.