As we didn't demonstrate the rounded corner feature during the Easy Tabs workshop, here is an example to complement the customization guide. This is actually very easy thanks to the excellent jQuery corner plugin used in the script.
The rounded corners are implemented in two of the Web Parts you received:
EasyTabs_CustomStyle.dwp:
$(".ET001_tab").corner("10px top");
QuickMenu_CustomStyle.dwp
$(".ET001_tab").corner("fray 8px");
To modify the style, use this page as reference:
http://www.malsup.com/jquery/corner/
For example, to get tabs with the top right corner cut, replace the line in the original code with this:
$(".ET001_tab").corner("bevel tr");
(tr stands for top right)
Remember to update the beginning of the script to point to your own versions of jQuery and jQuery corner.