The plugin does not work properly in WP 3.4.1.
The play button icon will show with a default install, but will only play the mp3 file once and then it becomes non-clickable. The playbar never shows up and instead just shows the filename in it's place.
I tried the fix that etellewyn posted in another thread, but it did not help.
Based on amount of support posts, it appears that this plugin has a lot of issues and is probably better labeled as an alpha or beta release, as it seems very version-dependent.