Even better (imo), we should just dissociate icons from viewers.

Much larger mime_drivers.php files.  You will have to define every 
MIME string twice - once in the icons array and once when defining the 
driver.  For a driver like the enscript driver (with 30+ MIME types 
defined), that is a lot of superfluous definitions.

It would be better to add an option to a driver configuration array 
that allows a user to disable the MIME Viewer rendering yet keep the 
icon definitions.  However, this will have to wait for Horde 4 because 
it will break BC.

Any reason not to prefill $mime_drivers['horde']['default']['icons'] 
with all of the MIME types we can handle so that the icons show up out 
of the box and let the other drivers override the icons as needed?

I thought this was in the FAQ, but I could be wrong.  Anyway, in 
horde/config/mime_drivers.php, just add an entry to 
$mime_drivers['horde']['default']['icons'] with the MIME types you 
want to define icons for.  i.e.
'application/vnd.ms-word' => 'msword.png'

Is there a sample of this somewhere? I didn't see anything in the wiki 
or the list archives.  I don't have wvWare, but I still want the Word 
icon.   Similar to how the PDF Viewer works.  Is the solution to have 
render() return $this->mime_part->getContents() if the binary can't be 
found?

Then alter your mime_drivers.php as appropriate.

I am using gollem 1.0.3.
I noted that when msword in mime_drivers.php is enabled, a nice word 
icon appear next to word file, but there is a standard text icon if 
msword is not selected; would be nice if the word ico appears even 
when msword is not enabled.