Recently I started getting involved with Fedora, mainly because of the GSoC 2013 program. It has a vast community with many developers and users who are always willing to help and that's the beauty with it :) I plan to be a package maintainer and get involved with the infra team.
Other open source involvements
I've been using Archlinux as my main distribution since 2007. I maintain several packages at the AUR and I try to contribute to the Archwiki whenever I can. I am also a member of an unofficial package team in Greece, where we serve a repository with popular packages that aren't in the official repos. I have also contributed to the localization of pacman and the AUR interface. Check my transifex profile. Recently I helped to package the snf-image-creator tool of the synnefo IaaS.
GitLab is an open source git repository application, built on Ruby on Rails. I have been using it since version 2.0 and started contributing as of version 4.0. In this page I keep track of all my patches that were accepted by upstream.
How Fedora, GSoC and GitLab are related? See here.