In my university years I would actually have preferred to have been able to study over the summer and get my degree done faster, but summer classers were only available if you could afford to pay up front and only certain subjects were offered. As for school students, I think long summer holidays are wonderful for them, giving them an opportunity to enjoy just being a kid outside of a formal educational setting. But then, I also think school is rubbish.
I think that it is really important for children to engage in "natural learning" - otherwise known as "life". For those who are not interested in full time unschooling long school holidays give children a chance to engage in this natural learning. Going on errands with mum and dad, helping out around the house, maybe going to work one or two days with a parent, doing the shopping, playing in the garden - these are all fantastic opportunities for learning. I won't say that the idea of having my children with me ALL THE FREAKING TIME is terribly alluring, but I truly believe that formal education falls very short of actually facilitating useful learning and I don't see any benefit to having children undertake more of it.
I think the school holidays are 2 long, esp' the summer ones. My husband is always commenting on this subject. 4 weeks max. And what was wrong with the 3 term school year? I see school kids going home at 1.30pm! I thought the school day was 915am-315pm! I think it's a lot longer is other countries.