Yoav Freund's original paper on Adaboost (note the title)pdf

There are better boosting techniques available, e.g. Gentleboost pdf, Logitboost (also in the same paper) pdf

Viola and Jones' original face detection paper pdf

A nice review of pre-viola-jones methods for face detection pdf

Adrian Oceanu sent me a pointer to this hilarious video. A team in India has used an automatic face detector to add mustaches to people's faces in realtime.