Vermont began allowing same-sex couples to form civil unions in July of 2005. There were roughly 1700 civil unions per year the first three years, most of them women. Here’s a retrospective from the Bennington Banner.
The statistics aren’t available for the last two years. Anecdotally, the story quotes town clerks as observing a lessening of the early rate of demand, perhaps because other states like Massachusetts allow gay marriage. There were threats of violence posted on the Internet in the early days, but that has lessened now. To date, the story says, there have been relatively few filings for “dissolution,” the civil union equivalent of a divorce.