It sends information about installed packages (but this is disabled by default, you can enable it using sudo dpkg-reconfigure popularity-contest) for package popularity/usage statistics.
The popularity-contest package sets up a cron job that will periodically
anonymously submit to the Ubuntu developers statistics about the most used
Ubuntu packages on this system.
This information helps us making decisions such as which packages should go on
the first CD. It also lets us improve future versions of Ubuntu so that the
most popular packages are the ones which are installed automatically for new
users.
It sends information about installed packages (but this is disabled by default, you can enable it using
sudo dpkg-reconfigure popularity-contest) for package popularity/usage statistics.https://help.ubuntu.com/community/UbuntuPopularityContest
http://popcon.ubuntu.com/
Package description: