In 9 Fascinating Things You May Not Know About the Penis, Liz Langley reports that smoking increases impotence by 30%.

Web M.D. Jeanie Lerche Davis reports that a study of Chinese men found, among other things, that “Men who currently -- and formerly -- smoked were about 30% more likely to suffer from impotence.” Smoking and erectile dysfunction are both connected (individually) with plaque that builds up in the arteries: it restricts blood flow and potentially causes ED, among other problems. The habit could also be making your erections smaller. 

Men’s Health reports in 8 Strategies for Stronger Erections that "In addition to damaging blood vessels, smoking may cause damage to penile tissue itself, making it less elastic and preventing it from stretching," says urologist Irwin Goldstein.

So where there’s smoke…there may not as much fire as you’d like.