The callouts are implemented, but the pictorials don't show by default (hence they don't appear to be replaced). If you turn on icons, then they show up.
To turn on icons, put this attribute entry in the header:
Or pass this flag on the commandline.
You need the callout icons from AsciiDoc in the images/icons directory.
In 0.1.2 I'm adding support for CSS-based callout icons.
If that doesn't work, could you post a sample?
I agree, callouts are very essential. They are among the top reasons I selected AsciiDoc.