Interesting topic. It might not be a bad idea to take the temperature of the fan base at present.
I haven't really moved across from anything, since my current esoTalk forum is the first forum I've had up and running for any length of time. But I've been playing with various forum scripts for a few years now, trying to decide which one I'd eventually use.
In fact, some folks may recognize my name from the Xenforo forums, since there was a time when I was planning to make available a Japanese translation for that script. Unfortunately, some odd compatibility issues with the TinyMCE editor they were using forced me to back-burner that project shortly before my translation was complete. When I found myself in need of a forum script and started looking around again in earnest, a couple months ago, I tried doing partial translations of several scripts, but eventually decided that esoTalk (and eventually Flarum) was the way to go.
Berlyn What does Flarum offer that your previously preferred forum/bulletin board software does not?
The main thing I like about Flarum is the minimalist approach. I think a forum should be about what its members have to say, and not so much about what the forum software can do. Keeping things minimal means that you can get by with lower server specs (and since servers in Japan tend to cost a lot, that's important). It also means things like sparing use of language in the UI design, which will make translations easier to complete and maintain. Most other programs I've looked at not only have features that I don't need, they also have a lot of language to explain those features. That's a lot of extra work that I won't have to do.
Berlyn What are some features currently available in other software that you think could benefit Flarum
Since the minimal approach is why I like Flarum, I'd be shooting myself by listing a whole bunch of features I'd like to see in it. That said, I think that some sort of effective spam control will be a definite must, and I'd also like it if Flarum had some way of logging IP addresses to make it easier to keep the forums secure. These things aren't a great necessity our current site, which is invitation-only. But as I think about our plans for opening a more public forum, where we won't be able to lock down registrations, I get the feeling that I'd like to have more security-related features than esoTalk currently offers.