There's been a lot of flirting going on in recent months between Apple and Facebook. In February, Apple CEO Tim Cook told a group of investors that Facebook was "the one company that is closest to being like Apple". Last week, Apple did a big App Store promotion for Facebook's new Camera app, and clearly knew about it well beforehand. Then, of course, there were Cook's comments at the D10 conference earlier this week. "Facebook is a great company." "And the relationship is solid." Not to mention the ever-provocative "stay tuned." Now the two sides appear on the brink of formalizing the relationship.