I work at a teaching hospital in the ICU and we have NPs, particularly in CV surgery and pulmonary. During the day, the NPs I've seen mostly assist in surgery and round on surgical ICU patients. At night, the NPs actually do quite a bit more. As we all know, in a teaching hospital, the residents are the ones running the show at night (with the attending on-call). The NPs usually have more experience than the residents and end up doing difficult intubations, central line insertions, etc., if the residents failed the first attempt. It's a fairly collaborative environment. During the day, they do multi-disciplinary rounds each day with the attending, fellow, residents, med students, NP/PAs, dietician, PharmD, respiratory & PT/OT.
As far as pay, there is a pay scale based on years of experience. Most of the entry-level NPs in ICU were ICU RNs prior. There are some NPs who are hospitalists in the step-down & med-surg floors, but I've mostly seen them at night. The ED & trauma units have NPs 24/7, but it's definitely a good mix of NPs & PAs.