Much like Roxy, my husband would bring it up as part of our foreplay. At first, I was a little turned off by it...over time it began to sound really interesting and then became a huge turn on. He never pushed the issue and let me grow into the idea. Perhaps I am slow, but it took me a full three years to be really turned on by the idea. Even then I did a lot of research on it to make sure that it would fit in with my moral beliefs. Imagine the surprise on his face when I said.."Honey, look at this website I found for swingers!" The rest is history.
Take it slow and keep those lines of communication open...ya just never know...
Lori