used to + do:"过去常常"表示过去习惯性的动作或状态,但如今已不存在。
Mother used not to be so forgetful.
Scarf used to take a walk. (过去常常散步)
be used to + n/doing: 对……已感到习惯,或"习惯于",to是介词,后需加名词或动名词。
He is used to a vegetarian diet.
Scarf is used to taking a walk.(现在习惯于散步)
参考资料:http://zhidao.baidu.com/question/5058855.html