My past experience with Megabonus has been:

10,000 points for 7 nights in spring 2004 (I was silver.)
5,000 points after every third stay in spring 2005 up to 25,000 points. (I was silver.)
25,000 points for 15 nights in spring 2006. (I was gold.)
35,000 points for 20 nights in fall 2006. (I was platinum.)
35,000 points for 20 nights in spring 2007. (I was platinum.)

Except for the second promotion in 2005, when I was unable to get 6 stays in the promotion's timeframe, I have been satisfied with the Megabonus promos and have been able to get every other one. I knew there was no way that I could fit in the max amount of stays for the spring 2005 promo since I usually stay at least 2 nights for each stay, and I was not traveling that much back then.

Currently, I have the 35k/20 night promotion again, and I should finish it before December 1.