I was married for only a year when I got sick with Crohn's, so my husband saw me go from very healthy to very sick over a 7 year period. It broke his heart to watch me go through that, and he's been thrilled to see me so healthy ever since surgery. He doesn't even notice the bag, and there are ways to be intimate without it being so obvious (like wearing a stoma cap or a short nightie).
When it comes to meeting new people, I usually wait until I feel like we know each other pretty well. Then, I'll casually bring up that I used to be sick with Crohn's, but have felt great ever since I had surgery a couple of years ago. You'd be surprised how many people know someone with Ulcerative Colitis or Crohn's, and they understand what a debilitating disease it is. Even if they don't, everyone has said that they're happy that I'm not sick anymore. That's a great place to start.
Once you've shared that much, and they've been understanding, you can talk in more detail right then or at another time about how the surgery helped you. For example, in my situation, my colon was so diseased, that in order to live a healthy life, I had to have it removed.
People are always amazed when I tell them that I don't have a colon. Usually they'll ask if I have a bag, and I'll say yes. If I feel comfortable enough, I'll even show them the top of my bag. So far, everyone has been accepting, understanding, and amazed, because they had no idea! I think the main thing is to get to know someone first, and then wait for the right time to tell them.