Marriages vs. Civil Unions

This is not a question about the morality of same-sex marriages; there are already other threads where that is being discussed. This is a question about the legal ramifications, and I'm hoping some of you who are knowledgeable about the law might be able to clarify something for me.

As I understand it, one of the differences between marriage and civil unions is that the legal statuses and categories conferred by marriage are recognized in all states, whereas the statuses and categories conferred by civil unions are recognized only within the state in which the civil union was enacted. For example, marriage establishes kinship between the partners involved, and that kinship is recognized even outside the state where the partners were married. By contrast, civil unions (in those states where such a thing exists) establish a kinship that is recognized within the state in which it was enacted but is not necessarily recognized in other states.

My first question is whether the above description is accurate. My second question is this: now that four states have granted same-sex couples the right of marriage, does this mean that the legal statuses and categories conferred by a same-sex marriage in one of those states will be recognized in another of those states? If two women are married in Iowa, thereby establishing kinship with each other, will that kinship automatically be recognized in Vermont come Sept. 1?

I realize that there is little legal precedence for the events of the past few days, so maybe the finer points of the law are still being worked out. But it seems to me that if the legal statuses and categories of same-sex marriages are not transferable between the four states that allow them, then same-sex marriages are not yet different from civil unions.