The problem? Installing chromium.i586 pulled in nss-mdns.i586 on my x86_64 system. I installed nss-mdns.x86_64 and the problem went away.
Whee!
Want to use chromium on x86_64? Do this:
cat > /etc/yum.repos.d/chromium.repo <<'END'
[chromium]
name=Chromium Test Packages
baseurl=http://spot.fedorapeople.org/chromium/F$releasever/
enabled=0
gpgcheck=0
END
yum --enablerepo=chromium install chromium nss-mdns.x86_64