Dymero - 7:40 pm on Apr 26, 2013 (gmt 0) [edited by: Dymero at 7:42 pm (utc) on Apr 26, 2013]
+1 on taberstruths post. That's basically my answer as well. Despite their attempts to make you promote your own content with ads, Facebook has done pretty well for a free source and has had some success in converting as well (though not nearly as well as our other channels).
However, if SU is working for you, then I wouldn't ignore it. The more sources of quality traffic you can have, the better.
[edited by: Dymero at 7:42 pm (utc) on Apr 26, 2013]