Ahhh, the Double Points, Double Nights promo after 9-11. That was the first time I made Gold. Before that I split my business between Marriott, Starwood, Hilton, 6 Continents, and Indepenedents and B&B's.
Once I made Gold with Marriott, fewer than 10% of my stays have been outside the Marriott Rewards brands.
One small point - I think stays in the first quarter of 2002 counted toward 2001 AND 2002 for elite qualification. I did a number of stays in early 2002 for no good reason other than to ensure elite status for both years.