Matt Smith is the 12th Doctor, or at least the 12th regeneration.
David Tennant cheating death, blow a regeneration, making his Doctor both the 10th and 11th regeneration of the Doctor.
Yes and no, the way I see it. I think the Ten-to-Ten regeneration should count in some way, as should Eleven's little donation in The Angels Take Manhattan
. I reckon he expects that he doesn't have quite enough juice left for regeneration number twelve. But then, who knows just what happened with River's own regeneration energy in Let's Kill Hitler