I was doing green smoothies for a while, usually at snacktime. I really enjoyed them in the summer, when it was too hot for soup. I've just gotten out of the habit of having them lately; I didn't even have too many this past summer. I think I was eating more salads instead. I kind of get into moods with this kind of thing, eating almost the same thing every day for a long time, then change what it is I'm eating every day.
When I was doing the smoothies, I would add protein powder if I was having it for breakfast but make it without added protein if it was for a snack. I also did a very different fruit/veggie ratio than many are suggesting. Too much fruit at once, even with the protein powder, wrecked havoc with my blood sugar. So I used mostly veggies with just enough fruit to give it a little bit of a fruity flavor; about 4 parts greens to 1 part berries. Many of the recipes posted here seem to be about half fruit and half veggie, and that simply wouldn't work for me.