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.
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 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).