The last time I used the nanny service was a couple years ago now. I remember my sim family had infant boy/girl twins. The first one favored the boy over the girl. That one got fired. The second one favored the girl over the boy. That one got fired. So before I risked a third one completely ignoring both (like in sims 3) I said forget it and had one of my sims stay home.
I think there was another household where I had one who did nothing but argue with her boss for no reason whatsoever. She was fired.
I've also had it where I fired one and had the same one come back the next day.
I've had some creepy experiences with them.
As for the Butler, well, I admit, I forgot all about him, unlike the other games, he's a live-in and I often don't have the room.
I'm sort of afraid to do it now with Seasons. I'd hate to have a infant or toddler in the house and have the butler or nanny do nothing but the gardening (do they do the gardening like in sims 3?)