I relied heavily on v8 juice for the first 6 weeks of my weight loss plan (about 3 per day). It really helped with my vitamins, potassium, and was a good source of veggies until I got my routine and taste buds used to more fresh veggies in other forms. It was also a great replacement for my diet coke addiction.
After a while, I weaned myself off of it as the fresh veggies took over, and after I realized that the sodium levels in v8 were more than what I wanted. Now that I've almost completely eliminated added salt to my routine, the v8 simply tastes too salty to drink.
But I think it is a very useful tool along the way.