In a large bowl, cream butter and sugar. Add the eggs, one at a time, beating well after each addition. Beat in bananas and vanilla. Combine the flour, baking soda and salt;; add to creamed mixture alternately with buttermilk. Stir in pecans.
Pour into three greased and floured 9-in. round baking pans. Bake at 350° for 30-35 minutes or until a toothpick inserted near the center comes out clean. Cool in pans 10 minutes; remove to wire racks to cool completely.
For the frosting, beat cream cheese, butter and sugar in a small bowl. Add vanilla. Spread between layers and over top of cake. Sprinkle with pecans. Store in the refrigerator. Yield: 12-16 servings.