I've been using this code in my navigation bar since the 3.6.x days (and it still works on 3.8.6 PL1):
Code:
<td class="vbmenu_control">
<a href="search.php?$session[sessionurl]do=process&showposts=0&starteronly=1&exactname=1&searchuser=$bbuserinfo[username]">My Threads</a> /
<a href="search.php?$session[sessionurl]do=process&showposts=0&exactname=1&searchuser=$bbuserinfo[username]">My Replies</a>
</td>
The difference is $bbuserinfo[
username] instead of $bbuserinfo[
userid].