Preheat oven to 350. In a large mixing bowl, cream together butter, peanut butter, and sugars. Beat in eggs and vanilla. Combine flour, soda, and salt. Slowly pour into wet ingredients. Mix until just combined. Shape dough into 1 1/4 inch balls. Place on an ungreased cookie sheet. Bake for 8-10 minutes. Remove from oven and place a Hershey kiss in the center of each cookie. Let cool. Store in an airtight container.