J.M.
My DD started using a sippy around 6 months, when I started her on solids. She was breast fed, so the only time she got a bottle was when I needed someone to feed her for me.
Around 9 months, she started using regular cups. By the time she was 12 months, she only had sippies for car rides or riding in the stroller. They will make a bit of a mess until they get used to it, but they actually learn quite quickly how to use them. :)