In addition to the soft landings mentioned above, I have also found they bump you back up to your old status quickly as well.

I was plat in 2000, 2001 and 2002. In 2003 I only stayed probably 20 nights, and they kept me at Platnium for 2004. In 2004 I only stayed probably 10 nights, and in 2005 they dropped me to Gold.

In 2005, after I stayed 25 nights they bumped me back up to Platnium (in June). So even though I'd only stayed around 45 nights in two and a half years, they bumped me up to my old level.