Ok, so it isn't much of a controversy but it will be missed. What's that? I am referring to the display when using the Windows Defrag.
Thinking back to the days of Windows 95, an operating system that definitely benefited from the occasional defrag process, it was mesmerizing watching the squares fill across the screen as the system was defragmented. With a Win95 system, the best way to get a real benefit from the process was to close all programs and, with everything else closed, what else was there to do but watch the colorful process?
Although I soon realized that it was not necessary to watch the process, which could take a considerable amount of time in Win95, as evidenced by the comments in Ed Bott's "Adios, Defrag display" and Robert McLaw's discussion in "Vista's Powerless Power Users: Someone Neutered My Defrag!"
For the Microsoft explanation, see the Disk Defragmenter FAQ.
Personally, I have been using Diskeeper for too many years now to be concerned about the lost of the display in Vista.