There isn't a facebook app yet so I access it through the browser. I would be surprised if one is not being developed though.
Google is intentionaly dragging there feet in writing apps for Win8 and Wp8. this is a strategic decision that is intended to hurt Microsofts new efforts because they are in direct competition with Goolge. So much for Google's "Don't be Evil" mantra. That left behind when they became a publicly traded company.
You're completely wrong about sharing too. Sharing is massively integrated into Win8 and WinRT. Maybe you don't know all of the features yet.
I do agree with you on some of the Modern UI. Some of the apps are great but some of them are too blocky (like the browser). Microsoft should automatically sense whether you are using the device as a laptop or a tablet and adjust the UI accordingly. Maybe detecting a mouse or something with the gyroscope would be successfuly.
Win8/Metro is definitely a first generation effort and hopefully will be tweaked to make it better with each iteration.
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