I work in a medical ICU and we have the same approach that the majority of others have already mentioned. Most
of our patients are sedated on Fentanyl/Ativan or Fentanyl/Versed gtts, but that's only because most people get agitated when a tube and lots of pressurized air are being shoved down their throats.
However, there are those rare few who do great without sedation, and we don't mess with them if they are. It's less weaning to be done, and better for them neuro-wise.
For pts on continuous IV sedation, we "dose optimize" once a day - in other words, we turn off the sedation to observe how the pt tolerates it. If the sedation has to be turned back on, we turn it on at half the original dose, thereby gradually weaning them as tolerated. Plus, the docs have told me that studies show interruptions in sedation actually improves neurologic outcomes.
Also, sedation and even chemical paralysis is always used on our unit if we have to use an unusual mode of ventilation, such as pressure control, volume control, oscillation, or even if we are reversing the inspiratory/expiratory times, etc. Anything that would feel extremely unnatural or uncomfortable to the pt (at least, more so than your "normal" modes of mechanical ventilation).