The following program gives an invalid compiler error:

/Users/rog/src/tst.go:7: fatal error: method mismatch: T for *T

It works fine if the x declaration is changed to:
    x := T([]int{23,4,6,7})

package main
type T []int
func (t T) foo() { }
func main() {
    x := T{23,4,6,7}
    x.foo()
}

darwin 386
ffbf0900a20e+ tip