From the new paper "A Recipe for Success? Randomized Free Distribution of Improved Cooking Stoves in Senegal" by Bensch and Peters (March 2012).
And this data is surprising (almost incredible):
Exposure to resulting smoke leads to acute respiratory illness, and cancers, particularly among women cooks, and their infant children near them. Resulting annual mortality estimate is almost 2 million deaths, higher than that from malaria or tuberculosis.
In Guatemala several NOGs, have been working on this. I have not seen studies on the level of usage, or effectiveness. Nevertheless I have heard that there are several informal practices that make it difficult the adoption of new stoves. One example: traditional stoves generate heat, and families gather around the stove at night. The kitchen is a focal point. New stoves do not generate as much heat. Adoption depends on gradual behavioral changes.