There is responsible treatment of the earliest writings.
http://en.wikipedia.org/wiki/The_Original_New_Testament#New_Testament_manuscripts
I agree with BeDuhn in that the most notable translation problem with the NWT
is the addition of "Jehovah"s in the NT, which he says changes the meaning of a
lot of verses. Specifically:
Some other Bible translations have used "Jehovah" instead of the Greek word
for "Lord," "kurios," for New Testament quotes of verses in Hebrew that con-
tain "YHWH." The New World Translation also uses "Jehovah" that way 78 times.
It's a debatable thing to do since none of the early NT manuscripts have it,
but as it's normally done it doesn't make any doctrinal difference in identify-
ing Jesus.
http://www.tetragrammaton.org/divname.html
http://en.wikipedia.org/wiki/Tetragrammaton_in_the_New_Testament
More controversial is the apparent motive for many of the rest of the 237
cases (plus 72 in footnotes) in which the NWT NT replaces "Lord" with "Jeho-
vah."
http://www.freeminds.org/doctrine/jehovah/witnessing-the-name.html
http://www.believersweb.org/view.cfm?id=539&rc=1&list=multi
The JWs leaders teach that "Jehovah," taken literally, refers only to the Fa-
ther, and that Jesus is archangel Michael, isn't to be worshipped, and isn't
God. In a lot of NT verses "Lord" appears in all the earliest Greek NT manu-
scripts and could be, and usually is, taken by mainstream Christianity to refer
to Jesus as God, but the JWs leaders' stance has it that "Lord" in those verses
refers to the Father and not the Son. So the word "Lord" in those verses is re-
placed in the JWs leaders' NWT by "Jehovah" to bolster the JWs leaders' case that
Jesus isn't referred to in those verses or to be give the mainstream identifica-
tion.
In 400 other verses where the JWs leaders teach that "kurios" refers only to
Jesus, the JWs leaders' NWT has "kurios" translated as "Lord."
Jesus, as taught by the JWs leaders, is archangel Michael, a god in the figur-
ative sense, who was called "Lord" too much.
http://glenster1.webs.com/gtjbrooklyn6b.htm