R help - Sep 2012 - draw.key; getting grobWidth to respect fontfamily="mono"

Hello

Within my panel function, I am using draw.key to create a custom key for 
each panel. I'm trying to use grobWidth to calculate the correct width 
for the viewport, but it appears to be disregarding the fontfamily when 
computing the width. Attached is an example; any ideas what I'm doing wrong?

Many thanks
Ben
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: grobWidth.R
URL:
<https://stat.ethz.ch/pipermail/r-help/attachments/20120906/cfe0d2f8/attachment-0001.pl>

Update: seems one way to skin this cat is to add

   gp = gpar(fontfamily="mono")

to the viewport() call itself. If anyone has any suggestions for a 
robust way to extract this piece information from the key grob itself 
(it's nested several levels deep), I'm all ears.

Thanks
Ben