I was using this cool looking plugin for a few days but then I saw a spike in page load times caused by the images loaded from the plugin:
http://trick77.com/2010/01/09/page-load-times-when-using-wordpress-social-bookmark-plugins/
SexyBookmarks loads an image containing all possible icons, even if one only needs a handful of those images. The image is 190k in size!! I think the only way to reduce the size of the icon-image is to create a custom image with just the icons needed for a particular site, and to cache it.