Its very easy with a small skin edit to add the joined date back to topic view on 3.2 if you require it.

ACP > Look / Feel > Skin Manager > (choose skin) > Manage Templates / CSS > Global Templates > UserInfoPane

Find...

<li class='post_count desc lighter'>
   	     {parse expression="$this->registry->getClass('class_localization')->formatNumber( intval( $author['posts'] ) )"} {$this->lang->words['m_posts']}
        </li>
        </if>
    </ul>

Add this after the </if> tag but before the </ul> tag...

<span class='group_title'>{$this->lang->words['m_joined']}</span> <span class='post_count desc lighter'>{parse date="$author['joined']" format="joined"}</span>

So you end up with this:

<li class='post_count desc lighter'>
   	     {parse expression="$this->registry->getClass('class_localization')->formatNumber( intval( $author['posts'] ) )"} {$this->lang->words['m_posts']}
        </li>
        </if>
<span class='group_title'>{$this->lang->words['m_joined']}</span> <span class='post_count desc lighter'>{parse date="$author['joined']" format="joined"}</span>
    </ul>

Save. Quick pic:



You might want to add a <br /> tag or suchlike to space it out, but that's essentially it.