Firstly, thanks for an awesome plugin!
I've noticed that the method Simple Facebook Connect uses to generate Open Graph tags causes the post or page being displayed to be processed twice: once to extract the tags, and once to show to the user. This can cause conflicts with other plugins which trigger actions (such as sending an email or performing some other transaction) when their content filters or shortcodes are run. Most content filters work fine when called twice, but in some cases this causes breakage.
Would it be possible to generate Open Graph tags after WordPress has run its normal content filters, say by registering a content filter of your own with a high priority?
I like SFC, but the way content filters get called twice has caused me grief in the past, and it always surprises me when I get tripped up by this.