Gallup reports trend lines in its polling of Americans' reported sources of health insurance (or lack of insurance). The percentage of Americans reporting they have employer-based health insurance has declined gradually over the last few years from approximately 49% to 45%. Insurance via government program (e.g., Medicaid, Medicare) has been edging up and now slightly exceeds one-quarter of the population.
The percentage of Americans who report being uninsured has held steady at slightly over 16% from 2009-2011. Some elements of the 2010 Affordable Care Act (health care reform) have already gone into effect. However, as noted in the above-linked Gallup article, the country's persistent economic difficulties have presumably dampened any gains in health-insurance coverage thus far from the 2010 law.
ACA provisions that are most likely to reduce the ranks of the uninsured -- new mechanisms to purchase health insurance (known as "exchanges"), tax credits for many purchasers, and expansion of Medicaid -- don't go into effect until 2014 (implementation timeline).