Judging distance on the water is much harder than on land IMO. 150' is only 50 yards, not very far. When we were out on the Naswa boat last summer, a tourist was asking me if the boats around us were far enough away, as the skipper had mentioned the rule to them. I said the boats at that time were about 100 yards away (a sand wedge if you will)
People in small crafts tend to think big boats are too close. I think it's far more important to judge safe passage when boats are closing in opposite directions, or there's a crossing path involved. At that point, I throw out the 150' and plot a course that takes me further away to allow for adjustments if needed.
It's not really that hard to keep a 150' distance in most areas. The thing I see a lot more boaters doing now is to plot a course and stick to it, without regard for anything else. No course adjustments for oncoming boats, just dead ahead with their line. I try to be aware at all times of what's all around me, particularly from the sides. I also try to make course adjustments well ahead of time.
Many boaters need more time on the water, and need to be more aware that they aren't the only ones out there. Far too many people depend on the other boater to move out of the way for them, and many drive their boats as if on a two-lane highway in a straight line. A major part of the problem is lack of courtesy.