This has been something on my mind in regard to Christmas. 

On one hand, it seems easy to define, which is having lots of still without putting in much, if any, work for it.

But does the level of gracefulness also take part? What if a child has rich parents and lots of stuff but is completely grateful and generous? How much does attitude play in the role of being spoiled?

I say attitude plays a big role, you can get all the goodies out there, but if you really know the value of the things given to you and appreciate the things then you're not spoiled.

Parenting has a lot to do with it. I'm not going to go in to deep detail to what I think as I've only briefly covered the topic in one of my classes, but psychology covers these kind of topics.

http://en.wikipedia.org/wiki/Parenting_styles

Specifically "Indulgent Parenting" comes to mind.

I'd define spoiled as someone who has or wants everything and no understanding of the work and effort it takes to obtain a good or service.

I think mrstickball nailed it. When someone is treated very good--even better than they deserve to be treated. Then, when they are treated in a way that they deserve, or even the way a normal person would like to be treated, they are ungrateful and complain.

People who always get what they want but when things don't go their way they begin to bitch and moan.