Hi Hanspeter,
hanspeter.klapf(a)mag.linz.at wrote:
  For a private wiki (with different companies
involved), the use of
 email-addresses as userid would be great. Is there a possibility to
 achieve this? 
I read your message only today. Not sure if this answer will be useful,
but I have implemented such a mechanism for a customer. I just attached
the illustrating code to this Jira issue:
http://jira.xwiki.org/jira/browse/XWIKI-1493
Cheers
Stéphane
  Thanks,
   Hanspeter