(Tim) Often, our session wrestles with the question whether this or that baptism is valid. For instance, if a young woman has come to faith through the ministry of Campus Crusade here at Indiana University, following which several of her Crusade sisters baptized her in Showalter Fountain, should we require her to be baptized again for membership in Church of the Good Shepherd?
More common are questions related to the validity of baptisms done by churches holding membership in non-profit religious organizations where the marks of the Church are absent and the organization publicly confesses that, for instance, sodomy and baby-slaughter may be acts of faithfulness before God. From my years in the PC(USA), it will increasingly be true that baptisms under the aegis of these non-profit religious organizations and their affiliates are not done in the Name of the Triune God, but rather using the modalistic language of "Creator, Redeemer, and Sustainer."
Good brother, Andrew Webb, has a helpful blog where he recently wrote about this question, giving a history of the debate among Reformed churches with particular emphasis on North America, and linking to a number of helpful historic documents related to this matter...
Check out the comments section below his post, also. And in connection with the comments, when we consider how far beyond the borders of the Roman Catholic Church the invalidity of Baptisms extends, I'm not sure it's as easy as Pastor Webb tries to make it saying Baptisms are valid unless the church has officially adopted heretical confessions. Or rather, I should say I'm convinced it's not that easy.