I'm looking for thoughts and opinions on an issue I'm trying to resolve.  We are planning on converting our 150+ community websites to a dnn solution.  Our current systems use different databases for membership so there will be duplicate usernames across portals that will need to be changed when importing into the dnn membership.  When I first evaluated dnn, I tested to see if it allows duplicate usernames in different portals, but i used the same password as well, which allowed the creation of the account but I came to realize that wasn't the scenario I was looking for.

If I understand the correctly, the purpose of using providers is to replace core functionality without effecting the rest of the system.  So, am I correct in assuming that replacing the default membership provider with a custom written one is a possible solution to this issue?

If so,  is this a huge job?  Has anyone done something similar? 

 I realize, that every 3rd party module is different, but assuming they were written not directly accessing the data tables that most 3rd party modules would work correctly with a replacement provider? 

Is there an easier solution I'm missing?  We can change the usernames if needed, but with a few million user accounts to deal with, I'm guessing or first line support people won't be to happy.

Thanks for any thoughts or suggestions,

Steve