test site migrating 3.0 ning site
Ning To Jamroom
The Ning3 CSV also has their location (country, state, zip), gender and birthdate which are also saved in Jamroom.
If you just email them now and ask them to re-register on the new site, at a guess, only 10% to 20% of them will actually bother to do it.
One advantage of doing the import and using the JR Tool to send them their new passwords is that it only sends an email to those who have not already logged in at least once. This means that after a couple of weeks, say, you could edit the email content and use the tool again to resend only to members that haven't yet responded, so hopefully you'll ultimately retain a higher percentage of your current members.