looks like this applies to new MR members with a Flying Blue (KLM/Air France) account. A new account for a friend took 2 days to receive a confirmation to sign in online - the account is now showing gold status online!

http://www.joinmarriottrewards.com/flyingblue/FBG2/

As a valued Flying Blue member, you’ll acquire instant Gold Elite status and earn triple miles when you join Marriott Rewards — the free, award-winning travel programme that gives you more recognition, more benefits and more ways to earn miles at over 2,800 participating hotels worldwide in 68 countries at any one of our 9 distinctive and diverse hotel brands.

Here's how to get started:

Enrol As a new member in Marriott Rewards
Stay At any of over 2,800 participating Marriott hotels worldwide between 31 March and 30 June 2008.
Receive automatic Gold Elite status in Marriott Rewards and earn triple Flying Blue Miles for each of your stays between 31 March and 30 June 2008