I also got this, but I'm not sure it's a genuine email.
Clicking on the register link for the bonus did not take me to RN's actual site, with a request to login (as such emails tend to do) but instead to a site whose URL was "http://pages.exacttarget.com/MSO_Triple_All/" and a whole lot of other rubbish after that. The page that this displayed said merely:
Thank you for registering for the Triple Feature Bonus. You are now eligible to earn triple rewards every day from 5/30/11 through 6/30/11 when you dine at one of the participating restaurants listed in the email inviting you to register for the bonus. See the original email for more bonus details.
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Who can prove this isn't spam?