I would not seriously consider using it for a serious site, but it is ok if you want to have a practice at running your own forum and you do not want to shell out for webhosting.
I know of a similar site but they use phpbb-
forumup.co.uk :: Create Forum free Forums
This is copied from their homepage-
What is ForumUp.co.uk?
It is a site created by the authors of one of the greatest Italian web communities
www.raulken.it (more then 70000 users, around 2 million pages seen monthly, and over 100 staff members) that have put their experience in order to help all the people build their own forum and community without having to spend time and money (everything's free) on server, domain and software development.
Here forums are created using phpBB Technology on a server with 100 MB/s connection, 4 Intel Xeon CPUs, MySQL Database, Apache server and Linux system environment: this grants stability, speedy and reliabilty. All the data is processed with PHP preprocessing and transmitted compressed to increase performance and reduce costs. ForumUp grows every day according to the demands of the people using it.
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I use phpbb on my forum and it is a pretty good reliable piece of software and there are plenty of good modifications for it!