Gingrich won the South Carolina primary but the big loser was President Obama. As long as the Republican nomination is in doubt, Obama cannot run a negative campaign. He has to try to be positive. He already has his anti-Romney strategy worked out. The Obama campaign and its auxiliaries in the press, will attack Romney for being a wealthy venture capitalists and for being... different (code words for Mormon). Back when it looked like Romney would would sew up the nomination with South Carolina, I started to see columnists reminding us that Romney's great-grandfather had multiple wives (for what it's worth, so did Obama's father and grandfather). I suspect that Obama's State of the Union address was going to have some veiled references to Romney. But, with the nomination still in doubt, Obama will have to wait.
Worse for Obama, Gingrich's attack on Bain Capitol will make it harder for Obama to attack Romney. Gingrich's attacks already took enormous liberties with reality such as blaming Romney for things that Bain did after leaving Bain. The general rule of thumb is that if a candidate can survive an attack in the primaries then it will be useless in the general election. Think of Clinton's infidelities or Obama's lack of experience.
The same is true if Gingrich is the nominee. By airing an interview with Newt's ex-wife just before the primary, they proved that voters don't care how despicably Gingrich treated his ex-wives. During the 1992 primary it came out that Clinton had cheated on Hillary multiple times but he survived it. Newt can, too.
Another problem for Obama - as long as the nomination is in doubt, the Republicans take center stage on the nightly news and Obama is an afterthought.
An extended primary also helps the candidates hone their message. Romney is a better candidate than he was four years ago. His earlier run helped him. This is Gingrich's first run and he entered late so an extended primary will help him, also.