My wife has never "not been on board," but she has not really shown much interest in reading through the posts, learning the details, etc.
She grew up with her dad handling the family budget and everyone else just not really aware of how it all worked. Dad made a financial decision and everyone else was on board. (Her parents' system isn't necessarily a bad one, but it has not done the best job in preparing my wife and her siblings for dealing with finances.
I started reading MMM a year and a half ago, and got really into it. I showed her the site, gave her the cliffnotes version of a few posts, and she was receptive to it but I could tell she wasn't going to read it. I have handled our finances since before we were even married (something she willingly and gleefully deferred to me) and she has agreed with most all the financial decisions I have made pre- and post-MMM. She has been on board with us saving for FI, as well as some of the approaches to doing so. She tries to help wherever she can (thrift stores, shopping with coupons, eating at home instead of eating out, etc.) but doesn't really make too many big financial decisions. Whenever I make a financial move (new credit card, new bank account, moving money between accounts, etc.), I always inform her of what I am doing it and why it will benefit us.
Slowly she has drifted towards a more frugal lifestyle without even knowing it.