I personally love my Vitamix. But it is darned expensive. I don't recommend it for everyone (click here to see my full review of the Vitamix). It's really only worth it if you see yourself making smoothies with whole fruits or frozen fruits often (as I do). These blenders do other tasks well, too, such as pureeing soups or making salsa, but cheaper kitchen tools can do those jobs (regular blenders or knives or food processors), so it isn't necessarily a good idea to buy a smoothie blender.
For me, it comes down to whether or not another kitchen appliance can do the job. Read my full comparison to make up your own mind.
Orange Smoothie image by Louis-Laurent Grandadam/Getty Images 2012, licensed to About.com Inc.