I don't exactly know what to post here so I'll just link you guys to the idea I had posted in the Template Modifications forums and how/why Jake thinks it needs to be made into a full addon:
http://xenforo.com/community/threads/default-avatar-based-on-link-custom-field.32836/#post-375314
http://xenforo.com/community/threads/default-avatar-based-on-link-custom-field.32836/#post-375314