First, John Shalf has used grdoc to document his SDS library for easy access to the HDF multifile interface. You can see the documented source code at the link to "Documented Source Code" on the SDS library page.
Secondly, I'm using grdoc to document grdoc! You can see the output from grdoc on the grdoc source code. Note that this uses some functinality (eg, perl support) which is still under construction, so Johns example is probably the better one. Also, the entire source is not yet commented. (I couldn't comment it as I wrote, since I didn't have grdoc around when I was writing grdoc!)