I've also started 
http://projects.theforeman.org/projects/ofi/wiki/Implementation_Notes 
page at our wiki.
BTW Redmine can be set to send notifications about all wiki
modifications. It can be done on 
http://projects.theforeman.org/my/account page. Choose "For any event on 
the selected projects only..." and then check box OFI.
If we decide to keep all the wikis with architecture description there 
uptodate It can be quite useful since every body will be notified about 
any design/architecture changes.
Petr