The marketing hype in the "What's new in DK 2008" section of the help file states:
Complete file and free space defragmentation in the most extreme of conditionsYou have to read this several times to find what they are actually saying. I think the crux is the word "can" in "Diskeeper can restore lost performance". It doesn't actually say that it will defragment a full drive, not does it guarantee to defragment the free space, although it gets quite close.
Diskeeper 2008 introduces the most powerful defragmentation engine ever developed. Even if your systems only have a percent or two of free space left available or a file in millions of fragments, Diskeeper can restore lost performance and save the applications reliant on those files from major reliability concerns.
This is just as well, because I could find no way of telling DK to consolidate all the free space and defragment my files. In the case of the C: drive (top image) I have clicked the "defragment" button a number of times but this is the best it can do. Oh, and the very large red file in the picture is a database file used by Microsoft SQL Server, a critical business application.
In the case of my D: drive shown here, notice how the free space is distributed in chunks all over the disk. I also encountered a bug when trying to exclude several .iso files from being fragmented. One of the files didn't appear in the directory listing. Weird.
The problem I have with all of this is that it appears that version 12.0.758 (DK 2008) is just a tweaked version of 11.0.709 (DK 2007). They claim to have improved the engine and the ability to defrag "nearly full" drives, but the results I am getting look remarkably similar to the results in the DK 2007 test, and my previous pictures using DK 8.
My conclusion: version 12 is simply version 11.2 with a different name, and a brand new price tag.
The most frustrating thing about Diskeeper is my inability to tell it to do what I want it to do. I can't tell it to move certain files to particular parts of the disk, not can I tell it to consolidate free space, or even to group regularly used files together. Granted, I can only do two of these 3 in PerfectDisk, but at least I have the feeling of greater control over what is going on.
I guess I'm not really Diskeeper's target market: I understand how the file system works and what can be done to optimise it. Diskeeper's target market seems to be the ignorant masses who neither know about nor care about defragmentation, and will believe all the marketing that is thrown in their direction. People like these who try to explain on the Chris Pirillo Show how DK works, but end up demonstrating their ignorance about what the MFT is. I know this sounds terribly superior, but I am a database programmer and I do understand defragmentation.
I will report back further once I have tested DK 2008 Pro Premier further.
Update: "3dprofessor.org" has published a full "review" of DK 2008, and Diskeeper UK informs me that they did not pay for the review. "He is just a big fan of our product".