Ya I use it, although I have little to no programming experience so the open source nature isn't useful beyond the fact that it's free. There is fairly decent support for it, and you can check the brewing software subforum and read the thread there.
From what I hear, it is fairly similar to BeerSmith, but I have no personal experience there, so you'd have to judge for yourself. I'm still a fairly new brewer but I haven't found anything lacking thus far.
The only problem I've run into thus far is exporting the recipe files. I can't get excel to recognize the file, and HBT won't allow it as a .xml upload. But I haven't reported any issues or done any realy looking in to finding a resolution, so it's possible that there is a fix out there.