It's interesting about Bishop Ussher, because we have had young earth creationists here who hew to the 6000 years old line, and others who are sufficiently, intellectually sophisticated to be embarrassed by that, and to simply make vague statements about "thousands of years rather than millions of years" (one member here who apparently despaired when Mr. Obama was elected--he's not been seen since just before the election--would use almost exactly that language).
The case of Bishop Ussher is interesing for another reason, and that is because it points up the ignorance so many religionists. Time and time again we've had young earth creationists here who insist on the 6000 years old position, but who have not actually ever heard of Bishop Ussher. Certainly they were also not Episcopalians.
You can see this ignorance, which many of them wear as a badge of honor, again and again. I can't estimate the number of times in my life that i've encountered people who will say "God moves in mysterious ways his wonders to perform.", and insist that it is a biblical verse. It's not, it's a line from a hymn by William Cowper written in the latter half of the 18th century. I've told people that and they've gotten angry about it.
Many, many christians are not only poorly educated, but they in fact consider that a good thing--as far as many of them are concerned, the only book they need is the bible. They could at least invest in a dictionary so they can understand all of the words they'll find there.