The advertising power comes from the Twitter userbase. Who will Uber be advertising to if they migrate the power users (mostly non-consumers) off Twitter?
One key point he makes is that your social groups are usually disjoint sets of people and you may not want to share the same information across multiple groups. For example, you don't want your family to see pictures of you at a wild party that your college friend tagged you in.
In the attribute box, clicking the arrow will flip it from up to down. If the arrow is pointing up it will rank high values better, if the arrow is pointing down it will rank low values better.
I agree. When I sign up for a service the confirmation email is generally already in my inbox by the time I switch tabs to gmail. Then the confirmation link takes me back to the site and logs me in, no hard work involved.
Also, I've never registered for a service and decided not to immediately check my email to activate my account when I'm prompted to. I can't recall a single time when I've come across a confirmation link while casually checking my email.
Especially in cities, where sharing photos with the people within 100 feet of you can include anyone in your 20 story apartment building. Even if the rate of obscene photos is low, just one could ruin the user experience.
Small UI bug I noticed, the icon in the Tail section for "top left" is the same as the one for "left top" (http://cl.ly/340F1H030G1s3D2F2F2H)