This thread is fantastic.

My wife lets me churn in her name now that we have taken a few trips in F. The only rule we have is that I apply for all the cards, make the reconsideration/cancellation calls whenever I can, and keep a matrix of when the annual fees are coming up for her.

As far as daily usage I am about in line with everyone else. I keep it simple, have her use the Sapphire for most purchases, and AMEX SPG whenever it's not dining/gas. If we have a minimum spend to get through I just tell her to use that card for a while.