The final results are in on the question How do you rate sky darkness?
19% don't rate darkness at all.
12% use the Bortle scale (read about this scale here).
48% estimate the naked-eye limiting magnitude (NELM).
19% use equipment that detects darkness in magnitude per square arcsec.
Sky darkness is a key component in planning visual and imaging observations. It is also an important statistic to include in logging observations. The 19% that don't bother to rate darkness could benefit from using one of the other scales.
Rating sky conditions could (should) be a matter of habit when setting up for a night's observing (or when imaging remotely). Including this metric in visual or imaging logs can help to identify conditions that work for you. If you aren't rating darkness, give it a try!