This page (http://www.8000ers.com/cms/everest-general-info-185.html) shows 4102 attempts to reach the top with 216 deaths last year. That puts it at about 5% of climbs end in death.

However, only about 2700 individuals climbed -- which puts the deaths / "uniques" back up to 8%. And if you assume that the sherpas die less frequently than do the tourists, 10% doesn't seem too far off.

Interestingly, K2 seems to be much more difficult with a much higher fatality rate: http://en.wikipedia.org/wiki/Eight-thousander