Unfortunately, the further you get from the Ning fiasco, the less people have been interested in conversion to wordpress.
I was able to use ning to buddypress plugin from WPMU DEV:
http://premium.wpmudev.org/project/ning-to-buddypress-user-importer/
I was not super happy with it, but I got most of the stuff moved with it. My biggest problem was that it emailed all of the users when I ran it. I highly recommend editing the source to remove that stupid feature, because there was no way to turn it off. I see no scenario where I would want to email all users before I even know if it all works...
I don't remember now if there were any other bumps, so I can't give it a full recommendation, but it might be worth a try... and as I recall, it was the only option we found, and it got enough done to get by. We did this 8 months ago...
We didn't use buddypress though. I am not sure if I installed it to convert and then uninstalled it, or if it just worked for all of the non-buddypress features (standard wordpress user info).
There was a post in the forum at wpmu dev about how to turn off the email feature.
Hope that helps...