A long time ago, disk storage seemed stuck at a dollar per megabyte. Now it's much less than a dollar per gigabyte, and that means most of us have nearly--or over--a terabyte of storage. It sounds wonderful, until you realize that can translate to hundreds of thousands, if not millions, of files, many buried deep in obscure directories where no sane person would ever venture. DiskAnalyzer Pro ($30, 14-day free trial) will not necessarily clean up your disk for you, but it will give you some powerful tools to help you in the process.
The interface is fairly simple and easy to use, despite a bit of clumsiness to the documentation. Specify a path (usually a drive root) and let it run. After a surprisingly small amount of time, it comes back with a very detailed set of reports on your hard disk. You can view, sort, slice, and dice the results in a variety of ways, such as finding all PDFs, or all files you haven't accessed in the past two years, or any other such combination. You can see which directories are the most bloated, or which file types take up the most space. You can do searches for duplicate files, and you may be surprised how many unwanted copies there are of some things.
DiskAnalyzer Pro can delete files, but you need to select them. For example, you might filter a list down to "All .xls files older than one year", then select them and delete them. DiskAnalyzer Pro will also move the files to the recycling bin instead of just wiping them, helping you avoid a painful "oops!" moment.
I did experience some issues. I was unable to delete some 0-length files in a search. At times, especially when building very long reports, DiskAnalyzer Pro appeared to be non-responsive, though it always came back to life when it was done. Most of the operations have either no or very limited feedback regarding the duration of the task. You'll see either be a dialog with no progress bar or just a "Wait" cursor, so you can't tell if you've got a few seconds or a few hours to go. Generally, I found DiskAnalyzer Pro to be pretty fast, especially given that the amount of junk on my hard disks gave other programs some fits. Last, a search is limited to a single drive at a time; you cannot specify "All local drives" or "Drive C and D". You can, however, specify a subdirectory--just your Documents folder, for example.
In comparison to some other programs, DiskAnalyzer isn't as visually interesting or intuitive as the venerable SpaceMonger, but it offers more robust analysis and filtering features. System Mechanic offers a basic DiskAnalyzer as a subset of its general functionality, but it is slower and much less detailed.
DiskAnalyzer Pro can be useful to a casual home or business user if they have a lot of files, or if they want to make sure that other users aren't storing unwanted data in an obscure subdirectory. It can also be very useful to an administrator who wants to see what's on other people's network drives.