Thanks for responding.   In my scenario, I am converting a couple hundred website, with varying numbers of user, from 10,000 - 400,000.  The current sites don't share databases so there will be thousands of duplicates when I try to merge them.  In my scenario we have no need to share users across portals as they are distinct sites with distinct users.

I'm trying to prevent the support issues with changing 1000's of users username and passwords, not to mention the headache of trying to find a friendly username after a few million have been used.

I looked at the getuserbyusername and it takes a portalid as parameter so I'm not why that would be a problem.   The aspnet membership routines seem to always use the application name which seems to be equivelant  the portalid.

As far as the management of the multiple profiles between different portals, that is a problem I have not solved yet.  The architecture is there such that you could build some sort of module to allow someone to manage their many profiles, but I have not done it yet.

I think I played with the DNNMasters Multi Portal User Sharing module and it offered an alternate Membership Provider.  Not sure though.  You would have to check it out.  I think www.dnnmasters.com is their website.