On the minus side, the U.S. taxpayer took on more responsibility. From WSJ:
Investors are worried that the U.S. government might be forced to take on all or part of the roughly $7 trillion of debt tied to Fannie Mae and Freddie Mac, the huge mortgage firms.
Fannie's and Freddie's debt obligations far exceed the total amount of federal government debt outstanding [emphasis added], which is $4.6 trillion, or about 40% of annual U.S. economic output.
Fannie's and Freddie's debt includes $1.5 trillion of its own debt instruments and more than $5 trillion in mortgage debt it guarantees. It also has $2.3 trillion in exposure to counterparties in derivatives contracts, according to independent research firm CreditSights.
Does this matter? Sure. There's nothing magical that says American government debt is somehow resistant to economic law and can never become a problem.