Stars: they're just like us! Getting chastised by photo sharing apps for posting supposedly inappropriate content.

Madonna posted a letter to her Instagram today that she received from the Instagram team. The letter warns her that some of her photos have violated the company's community guidelines, and reminds her to abide by Instagram's rules, such as not posting nudity or illegal content. It advises her to delete the offending content or else her account may be shut down.

It's unclear which photos violated the community guidelines. There's one showing Madonna's buttcheek but that's completely G-rated compared to other stuff on Instagram.

It is kind of refreshing to see celebs held to the same standard as regular users, but also--it's Madonna. Obviously, Madge herself scoffs at the idea of a startup trying to stifle her creative license. After posting an image of the letter without comment, all of her fans have commented things along the lines of, "UM H E L L O IT'S MADONNA."

Mobli, a photo and video startup that's no stranger to celebrity users (it counts Leo DiCaprio and Tobey McGuire as backers), released its own response to Instagram's celeb faux pas.

(Photo: Mobli)

Well, that's one way to go after celebrity users.

Ms. Huffington (flickr.com/worldeconomicforum)

The post-lunch session of the Guardian Activate Summit kicked off with an interview between Guardian U.S. editor in chief Janine Gibson and a woman whom Ms. Gibson called "the Madonna of our industry:" why Arianna Huffington, of course. Ms. Huffington, who donned a smart navy blue blazer and a perfectly coifed blond bob, introduced herself with some opening remarks about what she called the "fetishization of social."

"The fetishization of social is celebrating something going 'trending' or going 'viral' without asking what it is that's going trending or viral," said Ms. Huffington. "We all need to do a better job of asking those questions, otherwise we’re going to find ourselves in the same dangerous area that mainstream media have found themselves in, where everything is breaking news. Donald Trump endorsing Mitt Romney, Balloon Boy, all these things."

We found this comment especially pointed coming from Ms. Huffington, as The Huffington Post just tweeted, "Miley Cyrus saves a dog left outside of Walmart," a piece that has all the classic elements of a viral story (major celebrity + cute animal + feel-good component) without any of the explanation. We really do need to be asking why Miley Cyrus' dog saving abilities are going viral, wouldn't you agree?

After her lengthy self-introduction, Ms. Huffington fielded a few questions from Ms. Gibson. How did you feel when Obama made the joke about the Huffington Post winning the Pulitzer at the White House Correspondents Dinner, she asked?

"Any time the President of the United States jokes about your Pulitzer it’s kind of a good joke for me," quipped Ms. Huffington.

As always, there were the usual questions about whether The Huffington Post "steals" articles by aggregating them.

"The HuffPost is two things," replied Ms. Huffington. "It’s a journalistic enterprise--it employs 500 full-time journalists--and it is a platform. Even if I had a trillion dollar budget, I would always make sure Huffpost is a platform. We live in a link economy, and the joy of a link economy is that we can promise readers the best of the web, whether we produce it or link."

"Ubiquity is the new promiscuity," she added. "When people say they want to launch a site to show their stuff, that train has left the station long ago. Now it’s about, 'Can you put your stuff everywhere?'"

Ms. Huffington also said that maintaining a bootstrappy spirit is key to continued success. "I want us to keep that startup spirit even as we’re growing and scaling, because that’s really at the heart of staying ahead," she said.

Do you see any Lady Gagas coming to usurp your Madonna title, wondered Ms. Gibson?

"I think there can be room for Madonna and Lady Gaga," emphasized Ms. Huffington.

Quietly, almost as if she didn't want the audience to hear, she added, "It’s a very manly way of looking at things, like who has the biggest swinging dick."

Check out our coverage of the morning 2012 Guardian Activate Summit session with LinkedIn cofounder Reid Hoffman here.