If you stack a transparent stroke on top of an offset blurred stroke, you can achieve a pretty spiffy Inner shadow effect if you enable "Knockout group" on the object level in the appearance panel.
See the full image for a view of the actual appearance panel.
Extra tweaking can be done by adding a live "offset path" filter to the shadow-stroke.
*edit* now with the proper screenshot-attachment, fully expanded layer style! *edit*
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