On the whole, it seems a bit slow. For small or medium sites (a few thousand users, a few hundred thousand posts, its probably not much of an issue. Maybe a few hours at best.
However, even taking into account a few delays not directly related to the import, its taken over a day for me to import about 75,000 users and 1.7 million posts, plus PMs and other stuff.
The Cache Rebuild is also going really slow - at its current rate, its going to take almost 4 hours just to do the users - and then its got forums, threads and whatever else it does.
Based on this you are looking at a minimum of a few days to migrate a large site. Am I doing something wrong, or is this typical ?