We don't give our kids spending money just to give it to them. We start them out months away with a Disney earnings chart. We do give them gift cards at holidays, which gives them a bit more to use. This year the kids will probably be Disney rich b/c we have over a year of holidays and saving time! We usually give them $50 each as part of an early Christmas present. We don't pay for chores in our home, but they can earn money for doing our chores. We write it all down, and buy them gift cards to use. For our 2011 trip the girls earned enough to buy their own princess dresses, accessories, and Bibbidi Bobbidi Boutique hairstyle, nail polish, and makeup visit. They also had some extra for souvenirs. My son decided to not earn as much, so he was able to buy some stuffed animals beforehand and his Aerosmith shirt, guitar pick, and some additional items. Anyway, I'm just trying to give you an idea of what they took with them. I would say they each had between $150 and $200. Our 2010 trip they only had their $50 Christmas presents to spend.
As for us, we take about $1000 in cash and gift cards. We like to have a cushion just in case we need it. We still have to pay tips for ADR's and such, so we make sure to have a nice amount of money with us. We aren't lavish either though. We always have money in our account just in case we need it for something also. We like to charge everything to our room and then pay it down with gift cards. It's just so much easier, and we get fuelperks from Giant Eagle for buying the cards. Hope that helps.