I think it depends on what you are looking for.
In our case, we do not use the PS. Things were not hard enough for my child to put forth a meaningful effort in order to learn and he was developing a poor work ethic as a result. How my child was spending his days from 8:00 AM-3:00 PM began to matter to him at a very young age.
This was our case too - it was DS at 3.5 asking us to take him out of daycare/preschool and either stay home or change environments where he was not so bored.
It is definitely going to be dependent on your family, your school district and what is important to you and your children - family values vs what is taught in school, what is offered for acceleration, and the administration of the local school.
