When my son was born, my mum (his closest Grandparent) took on the responsibility of childcare so I could go back to work. She's stood by me almost as a second mum to him throughout the last 12 years. He goes to her house every morning and every teatime - whether she's babysitting or not - and is such a part of his life that, when I suggested we move house, he asked where she would live? (she lives next door at the moment!)
His relationship with his Nan mirrors the relationship I had with mine. Grandparents are that bridge between parenting and friendship. They can parent your child but advise them as friends, they're confidantes and the giver of treats.
My son called my Nan his Greater Nanny (rather than Great Nanny) as she was just the grandest person ever. And aren't ALL our grandparents the best?