By itself, I actually think it's a great name.
But it is entirely too associated with the pop singer. People will think of her in the context of Madonna before even the Virgin Mary (what the phrase "the Madonna" refers to). As with the names Beyoncé, Aaliyah (in the U.S. at least), and Cher, people will assume the bearer is named after the singer.
***
Please rate my personal name lists:
www.behindthename.com/pnl/69381www.behindthename.com/pnl/69381/117507www.behindthename.com/pnl/69381/109399hwww.behindthename.com/pnl/69381/132018http://greens-end.myminicity.com/