If you are making your smoothies a certain way they are most certainly good for you. Smoothies can be a great way to get your recommended servings of both fruit and vegetables into your diet. If you are using milk or yogurt in your smoothie you will also find that its packed with much needed calcium. Smoothies can provide you with all the essential nutrients that your body needs as long as you are putting the right things in. A wrong move would be putting in extra sugar or an excess of something like peanut butter as that can add too much fat.
On a whole just make sure you are adding healthy natural things to your smoothies as much as possible and they will present a healthy meal replacement or snack.