The most obvious downside of this approach is that it means you can only transfer files with a Mac (the desktop software is not yet compatible with Windows, although the developers are planning to add that funcionality soon) and that you'll need to have FileMagnet Uploader on any computer with which you want to transfer files.

But a desktop-based application does confer certain benefits. For one thing, you can queue files to transfer later by dragging them into FileMagnet Uploader: the files will begin to upload as soon as you open FileMagnet on your iPhone. And files transferred to FileMagnet keep a representative thumbnail--Files and DataCase both show only generic icons--so it's easy to browse a folder of images and find the one you're looking for, even if they have inscrutable names. Unfortunately, FileMagnet does not have the search or filtering capabilities of either of its competitors.

FileMagnet also has the best filetype compatibility of all three apps, reading not only Microsoft Office files, but iWork documents as well. It was the only one of the three apps I tested to display an RTF document with styled text. (Files displayed it as plain text and DataCase would not display it all.) The only file that caused FileMagnet to balk that Files and DataCase could read was a WAV file. I also ran into a repeated error message that FileMagnet was running low on memory when trying to view large images, but Magnetism Studios says this will be fixed in a forthcoming update.

At the end of the day, which of these applications you decide to use will depend largely on what kind of use you plan to get out of them. If you spend a lot of time transferring files to and from Windows machines, then Files and DataCase will make your life a little easier. If the ability to view as many different types of files as possible on your iPhone is your priority, then FileMagnet has the others beat. Those looking to maintain multiple volumes with granular permissions should look to DataCase. 

All three apps are compatible with any iPhone or iPod touch running the iPhone 2.0 software update.

[Associate editor Dan Moren blogs at iPhone Central and MacUser.]