Thanks to all of the responses I had on LinkedIn and by email from people who use DITA in their work, I have done a major revamp of the Companies Using DITA page on this site.
Not only does it list additional firms and organizations that were sent to me, but I have done additional research and listed firms that are referenced as being clients of some of the major DITA CMS software manufacturers. Also, using the mental images I was able to track down a copy of the Moldflow on the dita.xml.org site, which is no longer there. I added those companies I didn’t already have listed, though I checked to see whether they still existed, and in a few cases I had to drop a few companies that are either defunct (e.g. mental images) or have merged with other firms (e.g. mental images, Moldflow or Lombardi Software).
I have also added the industry segment for each of the companies in the list. This is tricky in some cases, since I can’t be certain with several of the larger conglomerates as to which part of them is using DITA XML. Where possible I use whatever default industry listing is given on Wikipedia.
The new version of the table is now driven by a database, which means that you can now do a search for a given company or sort the list by industry.
If you have any additional firms/organizations to add to the list, or if there are any corrections that need to be made, please let me know!