HTML is incorrectly stripped from description

Descriptions within Webform use the default input format specified at admin/settings/filters. If you need to use a certain HTML tag, you can add it to the default format (typically Filtered HTML). You can also use a "markup" component for extensive bits of HTML that use other formats.

just use firebug and web developer pluggins in firefox to identify a candidate class or id in the form and add some css rules to do it based on what you find that is unique.

<strike> may not work because it is not XHTML strict. If your theme is specifed as strict some browsers may not render it. Try using <del> instead.

Drupal.org is XHTML transitional though, so both of these show up:
Strike: strike
Del: del

Also, allowing users to post in Full HTML posses major security risks (to the point that they can take full control of your administrator account). I would highly suggest you use Filtered HTML with an extensive list of tags instead.

Wow, that is one nice looking Webform!

I tested this out locally and it seems as though Webform is being overly aggressive in striping out HTML tags, so there was no way this was going to work without a code change. Webform should be allowing any HTML allowed by the default format, but for some reason it has been stripping out most tags and then running through the default input format. This has multiple problems, the solution to which is just ensuring that we only run filtering on it once, not twice.

Apologies for the misleading advice, I've committed this patch to Webform 3.x and it will be in the next release. Thanks!