J.M.
My DD was using the straw sippy at six months... when I started her on solids. (She would get expressed milk in her cup when she ate her solid 'meals') Once she hit a year, I took away the straw cup and gave her a regular cup. She had a couple of messy weeks, but she mastered the open cup pretty quickly. Kids are able to do a lot of things... parents just don't realize it because we have so many fun gadgets to choose from to do things for them! lol. I get a kick out of it, because at 18 months we flew home to visit my family. My grandma gave my DD a sippy cup of juice, and my DD just sat there looking at it like, 'what am I supposed to do with THIS???'
Although... sippy and straw cups are very handy to have in the car!!! :)
(Also... my DD's speech therapist has recommended having her drink from a straw more often... It's good exercise for the tongue.)