I got that email too, but it came nearly three weeks after I got credited for the 5 nights to get my two Free Fridays. So for those who haven't gotten it, maybe there's just a lag between when you earn Free Fridays and when you get the offer.
It's tough.. I like Starwood, and especially the customer service, but Marriott has so many more properties and usually a little better rates, and on top of that they extended my Platinum status too. To complicate things further, sometimes it's a lot easier to stay at Hilton due to their location. Argh! I'm getting a headache.