I can't answer in detail for my wife - but since we started having anal sex about 3 months ago - she's getting into it more and more into it. In fact tonight she said 'I bet you never thought I would start to enjoy anal sex!'
To which I simply gave my standard response - "I told you so!"
I'm always up for anal! It takes some prep, of course, so it's better for us to say "Hey, let's have anal tonight ;D" rather than just go for it spur of the moment, but when it comes to willingness, anal play is always an option!
I have to be in the mood and very, very turned on. He will never just unexpectedly "stick it in" I have to ask (ahem..not "nicely" either more like demand) It rarely happens though, maybe once every couple of months because I prefer vaginal intercourse and usually anal only happens after I have had one or more orgasms.
I'm often in the mood for anal. My partner and i actually use it as a "warm up" before having PiV sex, like a type of foreplay. But of course this will only be done with my full consent, i dont like the idea of ANYONE just thinking that because we're having sex and know that i enjoy anal play/sex that it would be okay to just "stick it in" without getting an enthusiastic yes from me beforehand.