This morning was hair-raising.
Federico got the new version of GdkPixbuf checked in. But he forgot about the feature we needed for Nautilus. I was really worried for a little while. Eventually he sent me mail and said he'd take care of it. What a relief.
Well after I updated the GdkPixbuf use in three modules (gtkhtml, eog, and nautilus), I went back to async. metadata in Nautilus. And I managed to make it work! I'll be checking in today.