I once declared at the border in my car and was shocked at the price. As I recall it pretty much doubled the cost of the wine I'd bought in the US.

Oddly they have been more lax at the airport. I once brought 4 bottles, declared, and was sent to customs. The agent had me open my bag, looked at the bottles, and waved me through. He basically said it wasn't worth the trouble for that slight amount. More than 4 bottles, however, and he said I'd have to pay.

Obviously this is not a hard and fast rule and I haven't bothered testing it since.