As I said above, their October 2004 survey was the definitive source for the left on Iraqi civilian war casualties. They were also shown to have inflated those statistics by including every civilian death in the country into their casualty figures, regardless of the cause.
The Lancet is also a go-to source for Planned Parenthood and NARAL, mainly in the area of Emgency Contraceptives. The Lancet even went so far as to use its pages to suggest that Andrew von Eschenbach was an unfit FDA director because he was too beholden to Bush and his anti-abortion right-wing base (just the kind of findings you'd expect from a prestigious medical journal).
The Lancet also once announced a "near-unanimous scientific consensus that rising levels of greenhouse gases would cause global warming and other climate changes." Then they wrote a series of articles detailing how global-warming was creating a new generation of disease that would effectively obliterate humanity, thus affirming its existence (thus pinning it on greenhouse gases/mankind). These above-reproach findings were recently optioned by Al Gore, and are now playing at a multiplex near you.
My skepticism of The Lancet and its agenda is very well-founded.