Most people are conditioned from childhood to think that soap kills germs. Except for the occasional antibacterial brand, it doesn't. Well, not directly.
What soap (and shampoo) does do is remove the grease and natural oils that form on the surface of your skin. Bacteria and other microbes find a home under these oils and begin to reproduce. It only takes a few hours for these microbes to establish themselves across the skin of your hands or anywhere else on your body, once they've gotten a start.
Oil, as just about everyone knows, repels water, and this is how your body keeps your skin moist. Using soap to remove the grease and oils gives the running water from a faucet the chance to rinse the microbes off your skin. The water does the actual disinfection, not the soap.
In other words, an antibacterial soap isn't necessarily more effective than the ordinary kind. It gives you the excuse to be more lazy about how you wash, but as most people have heard in the newspapers by now, modern medicine is starting to lose its war of attrition against bacteria. You're just as well off if you use an ordinary soap, as long as you cover your hands with it thoroughly and rinse with water for at least 10-15 seconds.