I don't recommend using development versions. Although I guess times have changed a bit with softwares, and a lot of people go about using development or beta versions, it's a little different with a forum because of the fact that there's persistent storage which you can't easily recover. I use development versions of
Media Player Classic HomeCinema for example - because in the worst case, I just lose my settings (though this is doubtful cause it's unlikely there'll be a schema change).
Whilst I do try to make development versions stable, perhaps the biggest issue is that it's difficult to get the upgrader to work right. If I make a schema change, I add it to the upgrader so everything works out smoothly. However, with a development version, you may have half the schema changes of an official release, which the upgrader won't be able to pick up for you.
If you're comfortable with diff'ing the inc/xthreads/xt_upgrader.php file and reading through the PHP though, you can apply the changes manually.