An excellent article entitled "Creams Offering Lighter Skin May Bring Risks" appeared in the NY Times on January 15, 2009. While there are a few minor inaccuracies, overall, it is an excellent resource and a good introduction to the subject.
It is worrisome that over-the-counter products can contain potent topical steroids which, when used to the face and other thin-skinned areas for months or longer, can cause serious side-effects.
These pictures are of Sammy Sosa (before and after using a cream to "soften his skin" and a patient who used OTCs for her face which contained black market steroids and higher than recommended hydroquinone.