Currently we have two automatic welcoming extensions - HAWelcome and AutomaticBoardWelcome. The latter is a social tool, posting on the user's board, whereas the former is for normal talk pages.
@jack has an uncommitted and untested patch which makes HAWelcome not edit User: pages if the user has opted to have their user: page as the social profile page and the wiki page at UserWiki
We could attempt to go a step further though, and merge the two extensions so that HAWelcome will welcome users on their board if social tools are installed and the user has their social profile page as their default user page.