S.K.
If your daughter already has experience with full day programs- such as preschool or daycare- then I say go for it! She'll learn a lot more as long as you think she can handle the long days.
A friend of mine's daughter attended an all day kindergarten last year. She had only attended 1/2 day preschool before this and was overwhelmed by the long days. I don't think it was the time as much as how much she was expected to do in that full day. She learned a lot- but was exhausted by Thursday afternoon. She was miserable on Fridays and it took all day Saturday just to calm her down and relax her. It took her a few months to adjust. But she made out fine in the end.
I too am torn on the issue. I was lucky that our district only has 1/2 day- so it wasn't an issue for me. I held my daughter back one year- as she has a Dec. birthday- so I think she would have been fine with an all day program.
I guess it just depends on the child and how much experience they have away from home.
Go with your gut feeling.
-S.