I've always been keen on introducing new people to tabletop gaming. I'm not entirely sure how many people are interested in gaming, but aren't able (or willing, maybe) to find someone else to play with.
One of my first experiences with being a tabletop missionary was back when I was working at Game Towne in Carlsbad, CA. A couple of younger kids, probably in their early teens, came into the store. They were curious about role-playing, AD&D, etc, and they asked me to help them out. The first thing I did was introduce them to gaming using my own favorite system (at the time): Cyberpunk 2020. I prepared a short adventure and ran them through it after hours.
The next day, they came back and said they were hooked. They were more interested in a fantasy setting, though, so I pointed them towards Elric! by Chaosium. They bought it, thanked me, and I didn't see them again for another couple weeks. When they came back, they wanted more supplements. Seems they'd been playing almost daily since buying the Elric! rules.
It's been about 15 years since then, and sometimes I wonder if they're still gaming.
Another instance of this so-called missionary work was to introduce a few folks at my last purchasing job to D&D. I managed to get a group of three players together, and we played a number of games. Two of the three enjoyed it enough to continue with me; the third decided after her second game that gaming was pretty boring. We eventually pulled in a couple more people (one of my other co-workers, and the spouse of one of the others who'd already been playing).
As with all groups, there were personal issues that eventually arose that made things a little more complex. They weren't related to the game, but involved marital issues between one of the original players and her husband. It was also around that time that I got my offer to work for Mythic, so it was inevitable that the game was going to break up, anyway. Overall, I consider that experience to be a success, even though, to my knowledge, none of the folks involved (aside from me) continues to play D&D. If I'd remained at that job in California, I think we would've continued playing.
Now I have another opportunity to introduce someone to tabletop gaming. I'm looking forward to the chance. I don't know if the attempt will stick or not, but it's always interesting to see how things turn out while having a little bit of fun in the process. Let's just hope I'm not too out of practice to pull it off!