THis is an interesting article.
Check it out!

Hróbjartsson A, Gøtzsche PC. Is the placebo powerless? An analysis of clinical trials comparing placebo with no treatment. N Engl J Med May 24, 2001;344:1594-602.

Summary at the end of the paper says it all.

"When the data from each of the trials were pooled, there was no evidence of a beneficial effect of placebo in studies with binary outcomes, or in continuous outcome trials that used objective scoring criteria. There was a positive effect for placebo in continuous outcome trials with subjective assessment criteria (especially treatment of chronic pain), but this effect diminished with increasing sample size, leading the authors to suspect biased assessment in smaller, subjective studies.

The authors conclude that there was no obvious beneficial effect to placebo versus no treatment, and discouraged the use of placebo treatment outside the setting of a controlled clinical trial."