I consider it to be a prototype of what Penknife is supposed to be like, but with no module system or custom syntax. It's mostly for fun and so I have something to run when my only runtime is a browser, but I wouldn't be surprised if an s-expression parser over lathe.js turned into a pretty viable hack of a language.
The important thing for Node.js is that JavaScript has a nice Scheme-like evaluation model with a very high demand for fast implementations. It's at the point where they're practically putting it into hardware, which would essentially mean a new age of Lisp Machines. Pretty nifty and all. ^_^