The single best usage of the dial is scrolling while reading articles in Edge. Much better than the mouse wheel for lots of scrolling. A line or 3 is fine on the mouse wheel but for anything more and for long periods of scrolling (like reading) I much prefer the dial as it works wonderfully for that. Volume in Groove works well too. Brightness and zoom are just kinda "meh..." for me, but other's may have a different opinion. And that's like all there is to it *shrug* It seems like there should be more updates coming for it, especially at the OS level. I would have a hard time recommending spending $100 unless you were a graphical artist or a technology enthusiast who isn't afraid to blow $100 just to see what the new thing is like.
As for where I'd like to see it grow for me to utilize it more; I'm not sure that the two pieces of software I'd like to see coded for it will actually do so in the near future: Native Instruments' Komplete Control (software for use with my MIDI keyboard) and, well, any DAW really, but I'm currently playing with FL Studio 12.
The dial is easy to grab on the left side of my laptop keyboard the way I reach over to my right side for the mouse. And it lends itself nicely to any control that twists (obviously). For the MIDI keyboard and (virtual) studio knobs it would be perfect. Clicking with the mouse and spinning with the dial is WAY better than click-and-hold then slide-up / slide-down to change knob settings using just the mouse (that's basically how those controls are used, yeah =/).
It's interesting to note that I don't feel a need to have it on my screen even though it looks awesome for graphical artists to use that way. In fact it is perfect right where it is. Also, the MIDI keyboard has physical knobs but they are certainly not as nice as a single $100 knob
It's easier to reach for and use the Dial on the desk than the tiny knob on the keyboard. For me anyway.
I'd also point out that like most new things it takes getting used to - although in the case of the Dial it's not because there's any kind of learning curve (there wasn't any learning curve at all for me) but rather just remembering to USE the thing!
What I'd REALLY like to see is the following:
1 - Customization
The ability as a user to really customize the "custom tool" so that I can get it to work right in any software. I doubt this is simple, and it may not even be possible, but I'd like to get the turning of the wheel to work correctly and intuitively in any software (like those I listed above). I'd even settle for some kind of macro program to try and customize it to suit my needs - although the processing overhead with those things always seems to suck. I'd certainly give that a shot, but I admit it's just a guess that it would be helpful.
2 - Additional OS-level features
The other thing I would like to see is further integration into the OS. The custom tool is basic at best, and only replaces a simple keyboard shortcut. And can only have 3 at most so that is limited. It's also hard to imagine keyboard shortcuts that are better done on the wheel after long-press / selecting custom too / selecting shortcut. I actually think this can be done better, similar to the way headphones use a single button to do lots of different things based on the number (and length) of presses; I can see double-clicking the dial to get into a different set of commands for software (used with further customization listed above) and/or features like double-tap dial then scroll forward and back between desktops or open applications.
As a side note and to help gauge how I'm looking at the dial: My interaction with the computer includes a mouse, the keyboard, the music keyboard, the dial, the pen, and the touch screen. I'd probably be better off learning more vocal commands with Cortana. I certainly do like the way the OS is going and spreading out input / interaction scenarios. The dial is one more option for getting work done more quickly, intuitively, and reliably.