We've been using these for years, but wanted to know how well they really work. Our experiment involved two identical bottles of 2009 Old Vines Carignan ($6.99 each at Whole Foods) and a Vacuvin Wine Saver. After drinking exactly half of each bottle we sealed Bottle One with the Vacuvin and simply recorked Bottle Two, leaving both at room temperature.
After two days both wines still tasted good, though Bottle Two's flavors had developed more nuances. But after four days Bottle Two was clearly beginning to go off, whereas the wine in Bottle One still tasted fresh. After eight days, Bottle One was drinkable; Bottle Two was not.
Vacuum-sealed or not, we don't recommend keeping open wine around for eight days. But we're convinced that the Vacuvin does make a difference.