This is MOSS 2007 Enterprise on a publishing portal.

have you updated %system%\Program Files\Common Files\Microsoft Shared\web server
extensions\12\TEMPLATE\XML\DOCICON.XML with an entry for .pdf and added
pdf16.gif to the images folder?

You need a line: <Mapping Key="pdf" Value="pdf16.gif"/> in the <ByExtension>
section.

Yes I did. I followed these instructions  from MOSSChampions:

1. Download the Adobe PDF ifilter  6.0 from here

2. Stop the IIS Admin service: Start > Run > Services.msc >
Stop the IIS Admin Service

3. Run the Adobe pdf  IFilter 6.0 Setup program (ifilter60.exe)
to install the filter on the server.

4. Click on <Next> to continue.
5. Click on <Accept> to continue.
6. Click on <Next> to continue.
7. Click on <OK> to complete the installation.

8. Copy a GIF that you would like to use as an icon  (16X16)
in "C:\Program Files\Common Files\Microsoft Shared\Web Server
Extensions\12\Template\Images".

9. Edit the file C:\Program Files\Common Files\Microsoft
Shared\Web server  extensions\12\Template\Xml\DOCICON.XML .

Add an entry for the .pdf extension.
<Mapping Key="pdf" Value="icpdf.gif"/>

10. Perform an "iisreset" or recycle the SharePoint Application
Pools.

11. Add the .pdf file type  to the index list:
a) Go to Central Administration, then to the Shared Services
Administration Web of the current SSP, go to Search Settings and next
to File Type.
b) Add the new file type "pdf".

12. Perform a Full Update on the Search content indexes.

- My key reads <Mapping Key="pdf" Value="pdficon_small.gif"/>
Screenshot of my results.

I'm assuming this is on a 32 bit?

There should be reg setting to verify as well...

support.microsoft.com/default.aspx/kb/927675

Yes, 32 bit; Win2k3.

Thanks for the link. I had all of the keys, but there was one value I
had to add. However I am able to get results  from the pdf  documents.

Some things I found while investigating this: I went and ran a trace
against the content database for this site and what I found was
somewhat interesting.

In once instance, it is returning 9 results so I found the
SharedServices_SearchDB.dbo.MSSCrawlUrl table which has these 9
results returned  based on docid. (Found this via the trace) All of
the documents  that are returning as "empty lines" are actually word
doc files  (.doc extension, not .docx). When I follow the url that is
provided via that table, the files locate and open/edit/save just
fine. I could find no variation between those files and ones that
were returning properly. However, if I do a search  for those specific
files that are problematic in other searches, I get the empty  rows
again, they will not pull up. Other files from those folders in the
doc center pull up just fine. Very odd behavior. The investigation
continues.