Unrelated comment, but why is it becoming a design trend now to hide the scrollbars on websites? Luckily I accidentally hit the space bar, so I saw there was more content there, but without that I would have had no idea there was more information. I've seen this happen on a number of sites, so I don't think it's just Chrome failing to render the site. I just don't understand what possible reason there could be to deliberately hide the scroll bar.
I'm not convinced that I like Facebook or any of my friends content enough to want ANOTHER channel of absorbing it. However, the app seems to be beautifully executed and the marketing page is pretty flawless. Some of the memory concerns aside, I love when companies create those kinds of landing pages. Like this one: http://www.knocktounlock.com/