Jon restated the ideas I was trying to say in my post in a much clearer way. James has pointed out that it depends on "how good the data import person is and how much time they take to get it right." That is another way of saying the same thing; someone has to clean up the records that don't import well, and, like Jon, we found it easier in the long run to import minimal information that was easy to clean up, and then start fresh.
