I have been battling with a FusionBB 2.2 import for the past few days. It appears this particular import script may have a bug or two.
The main issue right now seems to be, units per page settings appear to not work on: User import
It appears as if the script just sits there attempting to pull all the data in immediately for the user import step of the process. The script cycles through correctly on forums and threads, pulling the precise number of forums or threads per page that you specify.
I have tried upping the my.cnf settings and that does help us get ~15,000 of the 18,500 users into the vBulletin database. But I can never get it to beyond 16,000 users. Is there any reason why user import doesn't cycle through 2,000 users (or whatever units per page) we specify? It just sits there attempting to suck in all the users as soon as you hit submit. (no what number you specify be it: 1, 50, 100, 1,000, 10,000, 18,000)