As someone who's played with it extensively (to the point of trying to build a new type system for it, though its slower going than I'd hoped as I lack the necessary skills currently, though I'm still working on it) -- it's library situation isn't as robust as I'd like. It's community is small but very fervent and super helpful (Araq and Dom are both amazing guys and will help you out in IRC whenever you need it). I'd like to see it take off more. Think of it like Go but with even more control over execution. It's a little rough around the edges, there are bugs, but it's usable right now. It's an awesome language and I love playing with it, even if you don't use it for anything in production I highly suggest using it just for the experience.
Have you tried using it in production (for some value of "production")? I wrote a web API "Hello, world!" in Jester about half a year ago as a way to learn a little Nimrod and at first glance found it to be a nice web framework.
Looking at Nimrod's AST macros (which I haven't used) I imagine Julia as a closer competitor to it than Go. They both appear to come from a "programmable programming language" mindset, though Julia arguably more so because it's homoiconic.
