Okay, miles can expire for a certain period of time! Question? If I would get Silver in November 2011 and not fly again till April or June 2012, that is technically still in my calender year, correct?

Also, If I would get Silver in November with an airline, as long as I use or earn miles within that year, I will not lose then. Buy, will they still allow me to keep my Silver status? For instance, I get status in November 2011, but don't fly in that calender year, instead stay at a Hilton or something, would I loose my status of Silver, but still keep my actual miles? I thought Graduate School statistics was hard to learn, that is nothing compared to an airline's mileage program....