Buettgens said outreach campaigns will make a dent in the uninsured. For example, major tax preparers plan to help determine their clients' eligibility for Medicaid or subsidies and steer them to enrollment assistance.

Maryland has its own marketing effort underway, and surveys will show whether they are effective, Sharfstein said.

That stability, however, isn't assured over time, potentially undermining efforts to insure more people. The bulk of Americans get coverage through employers, but people who frequently change or lose jobs or are self-employed often bounce in and out of coverage, Morici said.

He said studies have shown a lot of that involuntary movement, called churn. Hilltop, for example, found among Medicaid beneficiaries in Maryland in 2011 that about 20 percent were new to the program and 13 percent lost eligibility.

Buettgens expects churn to rise because there are more people eligible for Medicaid and subsidies. Officials estimate that close to one-third of people in any given year could gain or lose their eligibility for aid because of changes in employment or family status, making programs more costly to administer and interrupting coverage.

He said states and insurers were looking at ways to offer continuous coverage. One example is Evergreen, one of the insurers on the Maryland exchange. It has signed an agreement with a Medicaid manager that allows Evergreen customers who become eligible for Medicaid to keep their Evergreen plan.

Janet and Bob Anderson of Timonium spent time without coverage after moving from western New York to be closer to their children more than a year ago. They waited for Maryland's exchange to open to shop for new policies.

She said it was a "second job" investigating their insurance options on the exchange, qualifying for subsidies and signing up for a plan. But they are glad for the insurance they finally got the day after Christmas.

Janet Anderson, who runs a housecleaning business, acknowledged that she and her husband, a building contractor, "were taking a chance. I felt so relieved to get coverage because anything can happen at any time. This is one more thing off my shoulders."

Gruber, who works as an adjunct professor at several area universities, is elated with her new coverage.

But she said those using the exchange must be persistent. She was stymied for weeks after the site's Oct. 1 launch by technical glitches online and busy signals at the call center, but used Facebook to contact a "navigator" at HealthCare Access Maryland for guidance.

She was desperate to reduce her $520-a-month premium plus $300 for medications. She qualified for federal subsides on the exchange and will now pay $140 a month for medical and dental coverage.

"Is this better? Are you kidding me?" said Gruber. "A third of my income was going to medical expenses. I'm up to my ears in hock."