There are two functions here,

the first one will return the user url for a specified ID

function bp_core_get_justuserlink( $user_id, $no_anchor = false, $just_link = true, $deprecated = false, $with_s = false ) {

 global $userdata;

 $ud = get_userdata($user_id);

 if ( !$ud )

 return false;

 if ( function_exists('bp_fetch_user_fullname') ) {

 $display_name = bp_core_get_user_displayname( $user_id );

 if ( $with_s )

 $display_name = sprintf( __( "%s's", 'buddypress' ), $display_name );

 } else {

 $display_name = $ud->display_name;

 }

 if ( $no_anchor )

 return $display_name;

 if ( !$url = bp_core_get_userurl($user_id) )

 return false;

 if ( $just_link )

 return $url;
 return $url;

}

The second function will use the first, but get the url of the currently logged in user.

function bp_get_loggedinuser_link() {
 global $bp;

 if ( $link = bp_core_get_justuserlink( $bp->loggedin_user->id ) ) {
 return $link;
 }
 }