When I asked Patrick Blanche, of Hobbs+Black Architects, whether he saw good results from his use of Diskeeper, this is what he said: 

“Good results? … you mean GREAT right!  Allow me to explain,

We are an architectural business and work with many small interrelated files that can get highly fragmented, so for us using Diskeeper Server is a must to maintain our performance. For the past few years Diskeeper has been working full time on all file servers in Michigan, Arizona even Utah, and the result has been significant improvement in the user experience.  Back before Diskeeper, (a time I would rather forget) we suffered from literally days of waiting for Windows built-in defrag to try and cope with our TB size volumes.  Finally Diskeeper came along and we have seen those issues vanish.”

Then we worked up a fine case study about the performance benefits to his company and now they are deploying Diskeeper on all of their servers and workstations company-wide!  

The complete case study is located here: https://downloads.diskeeper.com/pdf/HobbsBlackSANCaseStudy.pdf