I'd done this a thousand times before, but had a bit of a moment and couldn't remember which file to edit. Having searched the Virtuemart Forums with no joy, I set about some detective work to sniff out where the file resided and what needed removing! The front page of your shop is styled using the template you're using which is selected when you edit your configuration - in most cases this will be set to "Default".
To remove the text which says "Categories" on the left hand side, below your shop description and above your category text/images, you need to edit the following file:
components/com_virtuemart/themes/default/templates/common/shopIndex.tpl.php
Around line 6 you should see the following:
echo "<br /><h4>".$VM_LANG->_('PHPSHOP_CATEGORIES')."</h4>";
This is printing whatever your language file has written for 'PHPSHOP_CATEGORIES' - in my case this was "Categories". Here you have two options, you can either remove that line in its entirety or you can edit the language file to have it display something more appropriate for your particular site.
