What's been missing is woolly mammoth nuclei with undamaged genes. Scientists have been on a Holy Grail-type search for such pristine nuclei since the late 1990s. Now it sounds like the missing genes may have been found.
In an odd twist, global warming may be responsible for the breakthrough.
Warmer temperatures tied to global warming have thawed ground in eastern Russia that is almost always permanently frozen. As a result, researchers have found a fair number of well-preserved frozen mammoths there, including the one that yielded the bone marrow.
We are getting nearer to the "can we do it?" part, but the question "should we do it?" remains. Link -via Metafilter
(Image credit: Wikipedia user WolfmanSF)