A magnum of wine is like a party in a bottle. So what does that make more than a hundred magnums? Some of the U.S. wine industry's biggest names turned up to find out at this year's Bring Your Own Magnum parties, hosted by Wine Spectator. The two annual celebrations, held on back-to back, food- and wine-filled nights in Sonoma County and Napa Valley, respectively, offer an unofficial kickoff to the weekend's Auction Napa Valley and its multiple events. The parties also give winemakers a chance to bring a magnum of their favorite wine and share it with friends and colleagues. Wine Spectator's MaryAnn Worobiec explains.