Greg Mankiw explains why a "public option" doesn't make sense and will give an competitive advantage to the government:

Even if one accepts the president’s broader goals of wider access to health care and cost containment, his economic logic regarding the public option is hard to follow. Consumer choice and honest competition are indeed the foundation of a successful market system, but they are usually achieved without a public provider. We don’t need government-run grocery stores or government-run gas stations to ensure that Americans can buy food and fuel at reasonable prices.
[...]
[I]f such a plan were desirable and feasible, nothing would stop someone from setting it up right now. In essence, a public plan without taxpayer support would be yet another nonprofit company offering health insurance. The fundamental viability of the enterprise does not depend on whether the employees are called “nonprofit administrators” or “civil servants.”

In practice, however, if a public option is available, it will probably enjoy taxpayer subsidies. Indeed, even if the initial legislation rejected them, such subsidies would be hard to avoid in the long run. Fannie Mae and Freddie Mac, the mortgage giants created by federal law, were once private companies. Yet many investors believed — correctly, as it turned out — that the federal government would stand behind Fannie’s and Freddie’s debts, and this perception gave these companies access to cheap credit. Similarly, a public health insurance plan would enjoy the presumption of a government backstop.

Make sure you read this column. In the public debate over health care, I'd put it in my top five of articles to read.

Also, the scholars from Cato have put together a video breaking down some of President Obama's claims from his ABC townhall.