Fellow Duke PhD student and Duke Newt contributor Matthew Thiessen has a fascinating article on Genesis 17:14 in the new issue of JBL. Thiessen argues that critical texts of this verse ought to read as follows (By the way, can anyone tell me how to use Hebrew and Greek characters in blogger? I don't know how so here's the translation):
And the uncircumcised male, who has not been circumcised in the flesh of his foreskin on the eighth day, that soul shall be cut off from his people, he has broken my covenant. (p.642 emphasis added)
The crucial part is "on the eighth day", which the MT and every modern translation I am aware of lack.
There are lots of reasons why this variant is important, but the thing that interests me the most is the fact that the longer reading is found in all extant LXX manuscripts, the Samaritan Pentateuch, Jubilees, (and possibly 8QGen frag. 4), and yet it is almost universally dismissed in favor of the reading found in the MT.
I don't think it's unfair to say previous discussions of this verse have relied on an uncritical confidence in Codex Leningradensis, and a corresponding excessive suspicion of anything that contradicts this codex. Check out Thiessen's entire argument to see why.