What's interesting about this decision is that it may open up the gates in the rest of Canada. The reasoning is that federal government has already accepted same-sex marriage in three provinces. The definition of marriage is a federal responsibility, and it isn't acceptable that something defined by the federal government should have a different definition in some provinces than in others.
The Globe and Mail (registration required, sigh, and what the fuck is up with that?), has a commentary by David Peterson which closes with this statement:
The ruling of the Yukon Supreme Court was a warning shot across the bow of the provinces and territories that do not yet recognize the right to civil marriage of same-sex couples. The decision says in no uncertain terms that they must begin doing so.