I just published an update (first one actually) to my music widget on the Android Market.
I received negative feedback (for which I am very thankful) about my widget, that it is not compatible with customized variants of the Samsung Galaxy S phone (such as Vibrant, Captivate, Fascinate or Epic 4G).
This suggested that the music player application on these models is slightly different than the one on the stock SGS. Since I only own an international version of SGS, I had to download official ROMs for those variants and check the differences in the music app.
It turned out that I was right - the music player on customized devices uses a little different package names (there might be other differences but this is the only one that matters from the perspective of the music widget compatibility).
I could not test these changes so I hope they bring actual improvements and fix the incompatibility. I only tested the new revision of the widget on my stock SGS.
Please report to me any problems with the music widget, especially if the widget still does not work on Vibrant, Captivate, Fascinate or Epic 4G variants.