It depends on the person's view of the JWs. Have they completely moved on, or do they think it is the "truth"? A few years back my sister (she left the JWs as well), started to get interested in a guy. There was something about him that caused them to click. Then one day I got to meet him, and instantly I picked up from the way he was talking that he too was a former JW. I even asked him, and he said he was. So I asked him about his views on the JWs and the Watchtower. His response was that he still felt like the JWs were the truth, and eventually he was planning on going back. When my sister learned this (she was there for the conversation), she decided to break it off. She had no plans on ever going back, and she didn't want to be tied down to someone who was planning on going back.
Now on the other hand, if the other person feels the same as you, it can be a good thing. My husband and I both were raised in it since we were both 4 years old, both our parents became JWs for the same reason, that was to survive the end of this system of things back in 1975. In his heart, he never believed them, but got baptized because of peer pressure from everyone in his congregation, including his parents. We both officially left the organization at the same time, and I will say it was very nice to have someone close to me that I could talk to about my feelings, and he could do the same with me.