Hi, studal, welcome to our virtual pub. Your question has been discussed at length--check the FAQ's, or do a search on oxidation, spoil, etc. The short answer is that yes, the bottle will go off after a while; how long depends on many factors, like how empty the bottle is, how often it is opened, how good the seal on the cork is, whether you have gremlins in your house, etc. I believe the chief culprit is simple evaporation of alcohol and perhaps other volatiles. There is widely varying opinion on what is a safe length of time to have a bottle open, but the consensus seems to be that when it gets much below half full, you don't want to let it die a lingering death. Drink up, and buy another one!