Did you hear that Lady Gaga was the magazine world’s No. 1 hit-maker in 2010? So says the Audit Bureau of Circulations, which found that the provocative performer sold more magazine covers last year than any other celebrity.

That got me thinking…Lady Gaga shares a trait with two other powerful women who are making news this week: Oprah Winfrey and Cathie Black, the new chancellor of New York City’s public schools.

That common trait? Reinvention.

Reinvention is more popular than ever because we’re in an era when traditions are exploding. Institutions are collapsing. You and the technology that enables you are mobile, meaning that anyone can redefine themselves. Go ahead, build your own brand.

Lady Gaga reinvents herself every time we see her — her perpetual reinvention is part of her shock-value allure.

Oprah, meanwhile, is taking her biggest risk ever by quitting broadcast TV and creating OWN: The Oprah Winfrey Network. Her new cable network reached more than 1 million viewers at its launch this past Saturday, at least when she was on the air. (And Discovery Communications , Oprah’s 50-50 partner on OWN, disclosed that it expects to earn a profit — by measure of EBITDA — in the first year.)

As I noted in “Oprah’s OWN moment” on Postcards Monday, OWN had been germinating in Oprah’s brain (and heart) for nearly two decades, but until now she didn’t have the guts to act on it and reinvent herself and her career.

The week’s other re-inventor, Cathie Black, headed Hearst Magazines for 15 years and, coincidentally, co-created O Magazine with Oprah. On Monday, Black stepped into her new hard-fought, high-risk public position: She’s overseeing America’s largest public school system.

So, it’s 2011. What are you doing to reinvent?