Note for GNOME Later than 3.6
1. libibus maybe compiled as a dependency of gnome, don't try to remove it (If you're not using gentoo, in gentoo you can disable i18n USE).
2. uninstall package that contains ibus-daemon on your system.
Or if you want to keep ibus installed (if you want to use fcitx you don't need ibus at all, for older gnome 3.6 you might also hit this bug, so you'd better remove it), run:
gsettings set org.gnome.settings-daemon.plugins.keyboard active false
as your current user.
3. If you are using fedora, make sure to use imsettings to select "Fcitx".