I was Peggy as a child, which I hated. I was named after my grandmother, Margaret. And she was an Irish servant. Her employers called her Maggie, without bothering to ask what she wanted to be called (Margy) and she really hated it, because it was a 'servant name', so she made sure I was Peggy.
I changed to Maggie when I went to college- I don't think there are too many associations with that name now. Most of my friends call me Mags, and my DH calls me magdelaina, when he's feeling romantic.
Margaret Mary is a total nun name, and I was frequently called "Sister Margaret Mary".