Documentation on the Wireshark wiki seems to not be really up to date, or at least it’s not completely applicable to Fedora 18, so here is what I did to make it work.
After installing Wireshark (and its GUI) with the usual:

yum install wireshark-gnome

It should automatically create a group called wireshark and we are supposed to add our user (mafio in my case) to this group:

usermod -a -G wireshark mafio
newgrp wireshark    ### used to force the new settings without having to logout/login

Then issue this last command:

setcap cap_net_raw,cap_net_admin=eip /usr/sbin/dumpcap
getcap /usr/sbin/dumpcap    ### used to check file capabilities

This is it, now Wireshark should be able to sniff network packets without needing to be executed as root.