Facebook Says 600 Million Use it on Mobiles Every Month

"As proud as I am that a billion people use Facebook each month, I'm also really happy that over 600 million people now share and connect on Facebook every month using mobile devices," said Mark Zuckerberg, Facebook founder and CEO. "People who use our mobile products are more engaged, and we believe we can increase engagement even further as we continue to introduce new products and improve our platform."

That, as much as anything, tells you the importance mobile now represents for Facebook, Google, Yahoo, Microsoft, Amazon, eBay and scores of other formerly "online" or "PC" companies.