rsvg-convert sends error messages about bad command-line options to stdout. This means that if you do

  rsvg-convert --some-switch-that-does-not-exist in.svg >out.png

you get no visible error messages, and an out.png that contains text!

I suggest this be changed so that error messages go to stderr. Might be as easy as the following, but I am not familiar with all the g_*() stuff, so there may be subtleties in there of which I am not aware.

--- rsvg-convert.c.~1~  2012-02-06 20:44:12.000000000 +0100
+++ rsvg-convert.c      2012-09-05 08:19:17.000000000 +0200
@@ -61,7 +61,7 @@ static void
 display_error (GError * err)
 {
     if (err) {
-        g_print ("%s\n", err->message);
+        g_printerr ("%s\n", err->message);
         g_error_free (err);
     }
 }