Tuning a radio by pressing keys or even mouse movement doesn't quite have the familiar feel of an actual knob. Griffin makes a nice knob called the PowerMate and I've now hooked one up to PowerSDR and it works well. Here's a demo.
While setting it up I learned of a great collection of keyboard shortcuts available in PowerSDR. I set the knob to send 100kHz up and down keys but in time I'll probably add accelerator modifiers for quicker tuning when needed.
There is a delay in the decode audio so you can't really spin the dial the way you would on an analog radio but perhaps a faster computer and lower latency audio driver will improve this.