Of course it is happening
There's wayyy too much marketing muscle and bedazzled managers about to not have it happen and, with mobile computing, there is a strong argument for it.
Of course, you also have the all those fingers looking for a new pie (mobile operators, handset vendors, tablet makers, etc).
It's the security aspect of the cloud that intelligent people are worried about, not its usefulness.
And given the amount of importance the security element has had in the evolution of Facebook, I wouldn't bet the farm on the cloud being any more secure than that.
But for the Facebook-sharing mobile tweeters, the cloud will be just peachy.