I assume the "seamless" part you mention here means that no extra window etc etc... except that after i click login, it's now going to wait for me to pull out my cellphone? What if it isn't around? What if i lose it or I am out of battery?

I mean from a geek's point of view, sure it's pretty darn cool (ps: I am a geek too!) But from a general user perspective, is it really that much more useful?