I'm joining the discussion, because weeds are pretty much non-existent in my garden. However, this was not always the case, and the answer to my problem was professional grade landscaping fabric. Keep in mind though, I garden in raised beds - not the native earth as most of you do.
Still, weed seeds will be blown in by the wind, and even dropped by birds - but they are so few that they stick out like a sore thumb. On average, I guess about 3 to 4 weeds per week are gently plucked from the beds, of which combined, measure around 180 square feet.
What most people don't realize, is that weed seeds are always present in the native soil, and germinate when exposed by tilling. Even though solarization will help, it can only reach a certain depth. Mulching is key, and if I had a traditional garden, cardboard or newspaper would probably be my choice.