I agree on both ends..from a daycare provider point of view I feel strongly about more than just a couple days a week to get the child comfy and felling more secure. However if the child needs socialization or time away from home (stay at home mom or only child) one day a week is better than "none" day a week.
I take care of my nephew one day a week for about 5 hours. His mom works from home and feels he needs some social interaction given he is home ALONE with her working in the other room! (dont ask) anyway..I think that is a great start for him. He is so alone all the time that if a child laughs in my dayCare he will begin to cry he is fearful of other children and extreamly cottled by his mother (when shes not working) my point: one day is better than nothing.