I noticed the Facebook Fan Box widget does not respect the width I'm trying to limit it to. So I tried adding a 'stand-alone' Like Box via https://developers.facebook.com/docs/reference/plugins/like-box/ and I found that the HTML5 version suffers the same issue. So I suppose it is not a bug in Simple Facebook Connect but rather a Facebook script related issue.
Maybe it'd be better to remove the width option from the widget completely? Or does it serve some purpose still?