I haven't, probably due in large part to the fact that the people I've actually met and enjoyed talking to since joining AN all live pretty far away. While I have met at least a couple of people who I would be interested in meeting in person and possibly dating, but none of them live in my area, so I can't imagine how much could come of that.
That being said, it's not that I'm totally opposed to trying to make a long-distance relationship work, I'm just trying to be realistic and admit that the chances are probably not great for a relationship like that to be successful. On the other hand, though I've not really dated anyone, so I couldn't know for sure, I do feel like I am fairly outgoing regarding things like this. If I were in a relationship with someone I truly cared about, I would be more than happy to do whatever I could to make it work, even if it meant having to drive for hours just to be with them.
I suppose the internet would be quite helpful as it would allow people to see and hear one another even from miles away, but even that isn't entirely the same as being with someone in person. I guess what I'm saying is, I'm optimistic, but not expectant. While I would like to find someone, I'm also realistic because I know that the chances of it working out are probably not in our favor. Still, I'm very much open to trying to beat the odds. ;)
I didn't meet anyone specifically through Atheist Nexus, but OKCupid.com may be a pretty good way for atheist and agnostic singles to meet each other. Being an atheist on that site has actually been found to correlate with a high response rate to emails. OKCupid is free, too.
Go ahead and try it, but there's a couple things you should know.
1) The sorting criteria are not absolute. Just because you may select (for instance) "non-smoker" in your matching criteria does not mean that they will absolutely rule out all smokers; apparently they use some formula whereby if someone matches a certain percentage, they will be presented to you anyway, even if they miss on one or two things. Same is true if you select "atheist"; you will still get a small number of people who match in every other way, but are not atheistic. I guess they're trying to present the widest variety of choices, but it's a bit irritating that there is no way to absolutely rule out any specific trait.
2) Similarly, even though you can pose your own questions and label certain answers as "mandatory", that doesn't actually mean that people who answer in other ways will necessarily be screened out. (Although it does raise the probability that they will be.) So just remember that "mandatory" doesn't really mean that.
Other than that, the site is a lot of fun, and does seem to have a large selection of people.