@ BrightlyBob - Not sure about the math though. I had 47 nights ending in 2009. With this math, I would have had 37 "bonus" nights; with the 47 nights in 2009 I should have had 84 nights and hence a Platinum membership boost. Instead I was bumped up to Gold.

If the conversion was done strictly on the actual nights stayed in 2009 then it makes sense because of the 47 nights, 15 of mine were by signing up for MR Premier Visa card. So, taking 15 away my actual stays were 32 nights : minus 10 would be 22 "bonus" nights + 32 actual nights in 2009 = 54. Hence my upgrade to Gold.