Only the authors should have user pages. But in K2 as it is, all registered users have their own page with a description and URL etc.

It would be better to have an option to remove this or instead link from registered users' names to their Jomsocial profile or phpbb3 profile etc.

I didn't want the user page available either, and I don't currently have any authors so I really don't have a need for the user page at all. I edited modules/mod_k2_login/tmpl/userblock.php and deleted lines 34 to 37; you'll recognize them when you see them (if not, let me know).

This will remove the "My Page" link in the user module. Not sure if that's any good to you or not, but it's a suggestion.