Is a Wine Country Passport a Good Deal?

Visitors to Sonoma and Napa Wine Country can buy passports that allow free tastings and discounted purchases at certain participating wineries. Are these passports a good deal? Locals say not necessarily: Only a few of the participating Sonoma wineries are worth recommending (like Sbragia and Papapietro Perry), while the Napa passport participants are especially disappointing and not worth your time.

Vineyard map from Sbragia