This plugin is great, and works fine with Widget Logic, but as of the latest versions of WP/ZigWidgetClass, it is not compatible with WP Widget Cache: http://wordpress.org/extend/plugins/wp-widget-cache/
If Widget Cache is installed & activated, the CSS classes in ZigWidgetClass are ignored when Widgets are displayed on the site (but they do show up the in Admin Widget screen panels)
Perhaps the author could check this out? Until now, the 2 plugins played nicely together.
Many thanks from all us WP devs!