The video quota only takes into account the size of <x id="START_TAG_STRONG" ctype="x-strong" equiv-text="<strong>"/>uploaded<x id="CLOSE_TAG_STRONG" ctype="x-strong" equiv-text="</strong>"/> videos, not transcoded files or user export archives (which may contain video files).
The worst-case scenario of an average person spying on their friends is quite unlikely. There are much more effective ways to get that kind of information.
The <x id="START_LINK"/>sharing system<x id="CLOSE_LINK"/> implies that some technical information about your system (such as a public IP address) can be sent to other peers, but greatly helps to reduce server load.