The links provided by JourneyOfLife above are instructive.
In light of the coming changes brought by Affordable Care Act, to shift Medicare and other tax revenues to expand Medicaid to those who are currently uninsured so they (in theory) won't rely on the Emergency Dept. (most expensive setting) for non-emergency complaints, these two illustrations are telling of the
behavior involved in gaining "free" or largely-subsidized first-dollar coverage:
And about the theory that providing publicly funded insurance (medicaid) to the uninsured will decrease ER usage by these recipients, because they'll now (in theory) have a primary-care doctor (never mind the existing shortage of those):
"Persons with Medicaid coverage were more likely to report at least one ED visit and multiple ED visits in a 12-month period than those with private coverage or the uninsured. This finding may reflect higher rates of disability and chronic conditions among persons with public insurance, including Medicaid, relative to the uninsured. However, uninsured persons under age 65 were more likely to have multiple ED visits in a 12-month period than those with private insurance. The data also show that persons without a usual source of medical care are not more likely to have an ED visit than those with a usual source of care, and that uninsured persons are not more likely than others to access the ED for nonurgent visits. Future work should focus on untangling the complex interactions among the sociodemographic, health status, and health care access factors that appear to be associated with visits to the ED.
From CDC - NCHS:
http://www.cdc.gov/nchs/data/databriefs/db38.pdf