Our then 1 year old used the nursery on the Wonder a couple of times back in September of 2013. We never had any problem getting reservations, in fact, one of the times, we just walked in and they said they could take him. I found the cast to be polite, friendly and caring. They listened very carefully to our instructions and were cautious about his egg allergy. We felt like it was very safe and secure, having to show our room keys and give the password when we picked him up. Now, we were lucky because being a September cruise, there were very few kids on our sailing, so he was typically one of two or three kids in the nursery, so he got spoiled, but I wouldn't hesitate to use the nursery again.
Hope that helps!