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Isn't this really similar to the sample widget?

Yes. But the sample widget provided by Automattic in the initial widgets plugin release didn't do what I wanted. I took that widget and made it much more configurable and feature-laden.

Can I style the widget's appearance?

You should have all the hooks for CSS styling that you need. The widget produces html with the following layout:

div#deliciousplus-box
 ul
  li
   img
   a.deliciousplus-post
   span.deliciousplus-description
   span.deliciousplus-tags
    a
    a
    a

With slight variations, depending on which options you have enabled.