Many years ago, it was possible (and perfectly acceptable) to drop into wineries for tastings without reservations. However, every wine region is different and not every tasting room is open every day. This can make planning a multi-winery trip difficult--especially if there are specific wineries that one really wants to visit.
While it is still possible to drop in for standard tastings at some wineries, reservations are required for many of the tours and events that wineries now provide: vineyard tours, cellar tours, cave tours, winemaker dinners.
With more and more visitors flocking to wine regions to enjoy the winery experience, it can be tricky to get into all the great wineries on your wish list. Until VinoVisit.com, it wasn't possible to schedule reservations online. Soon you can quickly search wineries based on the attributes that matter most to you (architecture, varietal, amenities, distance from hotel, etc.), and create an itinerary and map to share with friends or send to your phone.