I think it depends on your hospital and how well they can retain their staff.
I work in a hospital where we don't have staffing problems, as the hospital has great staff retention and they aim to please their employees, therefore people stay because we're happy for the most part.
I work in a level III NICU, in which we staff ICU babies as 1:2 or 1:1, depending on their acuity. Each shift we add up acuity points and the total number of points determines if the baby is "high", "medium", "low", or 1:1. So a high/low, medium/medium will usually be how the assignments are paired off.
Then in the intermediate nursery, we always have 3 babies. I've never seen it anything other than 1:3, except sometimes you'll see one of the nurses with an open spot, only have 1:2, then if a kid needs to be moved to intermediate, that nurse would then pick up the kid moving in.
Sometimes even with good staffing of assignments, your night could still be insanely busy. A couple of weeks ago I had a 1:1 that was so busy, I had people helping me constantly all night. So, a good support of co-workers is a must! Do you guys ever see a really sick baby that is assigned more than one nurse?!