We actually started looking into this today. In all honesty, I didn't know about the ipaddr field in the database.
Either way, we have some ideas of easy ways to add the ipaddress on registration, but it likely won't make it in until the 4.0 release expected next week. That release will also have the other fixes we've added to the CB plugin already on your site.
Just a few other questions about this field:
Is there any way to see the ipaddress field in Community Builder, or is it simply something you have to look in the database to see?
It's only set on registration, correct, not on every login?
Thanks,
Alex