My idea was that why do we have to invent a way to share the users across portals?  With the skinning capabilities of DotNetNuke reaching down to the page level, how about just applying different skins to groups of pages and have them all share the same portal?

This seems too easy at first, and I'll admit that I knew there had to be some "gotchas", but I volunteered to do this for the Milwaukee .Net User group web site (yes they really are still running on DNN 1.0.9) so I'm committed to following it through.

The first hurdle was to make different host.domain names point to different starting tabs instead of different portals, I thought about making different child portals for each one and then manually changing each of the different default.aspx pages to redirect back to a different starting page within the main portal.  That would work, but then I thought, why not just use the UrlRewriter, that is what it is made for.  That was the first "gotcha".  The UrlRewrite module only rewrites the path portion of the Url, not the host.domain name part, this is a simple fix though.  After doing that I can now add rules to the SiteUrls.config to have specific host.domain names start on specific tabs. 

Next up will be getting the menu to only display a specific root item and it's children depending on what skin I am using. 

Another thing I will probably want to do is to make some of the admin controls like Newsletter into regular modules so that I can add them into different pages and assign security for the admins of each group seperatly.  This wouldn't be required if you just had one administrator for all the groups or each group trusted the other groups admins at that level.

Anyway, just thought I would share the idea and see if anyone else had tried something like this.  I'll do a writeup of the complete steps for this when I get it all working.