The bike war has been raging on the local newsgroups for nigh unto a week now; here's another great article to add fuel to the flames.
Of all the transport systems available, including public transit, shipping, and rail, cars are unique in that terminal costs (doing something with your vehicle when the trip is finished) are offset to the rest of the economy. This 'provides a huge subsidy to motorists, and thus increases the demand for cars, parking spaces, and vehicle travel.'
Only walking, which has effectively no terminal costs, is comparable. All things being equal, most people would rather drive than walk. The problem is that all things aren't really equal; parking requirements just make it seem that way.
By breaking the relationship between use and payment, "free" parking eliminates the negative feedback that keeps the system in balance. As a result, everyone decides to drive everywhere, and the car crowds out other forms of transportation.