Facebook isn't the only one announcing impressive milestones today. Pandora announced at the New Music Seminar that it has 60 million registered users. That's not exactly Facebook's 500 million, but pretty impressive nonetheless.

It wasn't that long ago that Pandora's obituary was all but written, but things are looking bright for the company now.

Pandora's collection consists of hundreds of thousands of songs from 90,000 separate artists, and 80% of them are played every month, according to the company. As MG Siegler says, "Think about that compared to traditional radio, where you often turn it on and hear the same things over and over and over again."

No doubt.

"Pandora plays the music of tens of thousands of artists every day. It's a very promising sign for the industry that music fans are so quickly embracing this new form of radio," said Pandora CEO and President Joe Kennedy.

"The New Music Seminar convenes the architects of the next music business and Pandora is certainly one of them," said Tom Silverman, director of the New Music Seminar. "This milestone is a major building block in the foundation of the next music business. We congratulate Pandora on its achievement."

Not only are Pandora's mobile apps popular, but the company was one of Facebook's launch partners for the Open Graph, which likely provided a nice boost. With the Open Graph, users can see music their Facebook friends like on the service, which can make it even more fun.

As smartphone usage continues to rise, Pandora will probably continue to grow right along with it. As a mobile app, it's an easy, accessible way to take personalized music with you, and that is something that many find very appealing. As Siegler points out, Pandora is also looking to find its way directly into more vehicles and various other devices as well.