just found it out how to get default linear view ...

in /includes/thread.inc.php find ..

if($thread_display==0) $smarty->assign('subtemplate','thread.tpl.inc');
else $smarty->assign('subtemplate','thread_linear.tpl.inc');

replace with ..

if($thread_display==0) $smarty->assign('subtemplate','thread.tpl.inc');
else $smarty->assign('subtemplate','thread_linear.tpl.inc');

Typo? These are identical..

in /templates/templatename/subtemplates/subnavigation_2 find ..

{if $usersettings.thread_display==0}<span class="small"><a href="index.php?mode=thread&amp;id={$id}&amp;toggle_thread_display=true" title="{#thread_linear_linktitle#}"><img src="templates/{$settings.template}/images/thread_linear.png" alt="" width="12" height="8" />{#thread_linear#}</a></span>{else}<span class="small"><a href="index.php?mode=thread&amp;id={$id}&amp;toggle_thread_display=true" title="{#thread_hierarchical_linktitle#}"><img src="templates/{$settings.template}/images/thread_hierarchical.png" alt="" width="12" height="8" />{#thread_hierarchical#}</a></span>{/if}

replace with ..

{if $usersettings.thread_display==0}<span class="small"><a href="index.php?mode=thread&amp;id={$id}&amp;toggle_thread_display=true" title="{#thread_hierarchical_linktitle#}"><img src="templates/{$settings.template}/images/thread_hierarchical.png" alt="" width="12" height="8" />{#thread_hierarchical#}</a></span>{else}<span class="small"><a href="index.php?mode=thread&amp;id={$id}&amp;toggle_thread_display=true" title="{#thread_linear_linktitle#}"><img src="templates/{$settings.template}/images/thread_linear.png" alt="" width="12" height="8" />{#thread_linear#}</a></span>{/if}

Hmm. Is this still valid? I love the threaded index of my forum, but when people switch to 'Open in thread' I would like Linear by default.