When I was quite a bit younger (ouch!) and going to college, back in the early eighties, I basically only had one vehicle to drive around with then, so hard-wiring seemed more feasible.
Today, I travel extensively, use a host of rental cars, and use a variety of radar detectors in any given month.
If an when I drive through the great Commonwealth of Virginia (with my STi Driver, of course), I prefer a certain mounting location that is different than normal.
I also have incorporated Cheetah's GPSMirror into the mix along with their radar detector interface.
Given all of this, I have moved away from hard-wiring, although as you can see, my circumstance may be a bit unique.
Currently I have a much older K40 model, a "remote" that's been hardwired, however, that will be giving way to either an STi-R or Escort's future SR series replacement remote radar detector.