If you can untap her and use her ability multiple times in a turn, she can become really abusive. Obviously, she was way too fragile for Standard play. But from day one, Azami, Lady of Scrolls decks wanted to play this. It's not just because she's a Wizard, either. Azami plays so many Wizards that you're going to pretty much always steal the best opponent's creature every turn until someone finally knocks off the Beguiler of Wills. Lots of Commander decks can use her, although she's not a staple anywhere. She's pretty annoying, and that's just awesome.