Wireshark Setup
You don't need to manually add the "wireshark" group; dpkg-reconfigure does it for you. Try removing the group (and your user from the group), run dpkg-reconfigure, add your user back to the group, and then, re-login. I verified these steps in Mint 12:
$ sudo apt-get install wireshark $ sudo dpkg-reconfigure wireshark-common $ sudo usermod -a -G wireshark $USER $ gnome-session-quit --logout --no-prompt # Assuming you're using Gnome $ newgrp wireshark