Karsus responded: They are destroyed anyway so what is the harm in using them for research?
I would assume from your response and question that you already think that creating embryos in vitro is wrong, but because they had already been created and subsequently died, why shouldn't we use them for research?
I would submit that using these "byproducts" of creation (although, IMO in vitro fertiliation is an evil, but non-the-less life is created) for research simply helps "encourage" the creation of life simply to destroy it for research. This is a terrible, terrible, road to go down. Didn't the Nazi's play similar games with studying/experimenting on twins, and "playing" with genetics in trying to create the "super race"?
This is really no different than using the fetus from an abortion for "harvesting" organs or tissue for research. If you believe life begins at conception, then using the remains of a human being that has been conceived (whether by "normal" means or "in vitro") for scientific experimention is wrong. (IMHO).