I think about a new hook point.
When user save his settings in profile is nice to add a hook point. Why? Well, with this hook point, integration between for example frontpage and board will be nicer. I was wrote an application in Zend Framework for a main site and I need to integrate settings and profile fields like user IM accounts etc. between main two applications. Sync action can be executed when user changing his settings.

PS. Sorry for my English :-)

The hook point already exists.

http://community.invisionpower.com/resources/documentation/index.html/_/developer-resources/custom-applications/membersyncphp-r8

You would use the onProfileUpdate method.