Not a compelling offer. Yep, it's the same RewardsNetwork group that runs this for all of the major airlines, Hilton, and others. With the current "limited time" offer, Marriott's giving you 8 pts per $ spent...which works out to about 5% cash equivalent back. Rakuten (formerly eBates) will give you 5% cash back all the time if you use them as your target for RewardsNetwork.

It also looks like the intro offer isn't valid for any of us who already use RewardsNetwork with other targets (ie: airlines/Hilton/etc).