Aaron is the guy doing this for us, and he is quite good at what he does.  For some reason, my blog gets to be the test dummy, I guess I am the loudest (not).  This is a really interesting read if you are into reading code.  If you are not, then just pass, and scroll on down to the cheerleader and puppy pictures :)  Here is a snip of his article:

As a first run, we imported a blog called The Beauty Blog.It was noted that it did not appear all comments were imported as therewere some missing. As a point of reference, one entry on the originalblog entitled My Solution for Buildup had 4 distinct comments from 2 users.

However, upon import and viewing in the new WordPress blog, only 2 comments showed up by the same user” http://www.technosailor.com/