Out of the box it works really well, but I ran into problems when I tried adding multi-process support (via the cluster module) to my app.
So I created a little wrapper script that uses a lockfile to allow each process to access the database without stepping on each other toes. I've uploaded the code to GitHub at [removed]. As of right now it's not a package that can be installed via npm but if people are interested I might go through and make it one.
It's working for me in my app right now, if you like it let me know. If you find a bug please submit a pull request.
After further testing I've found that my wrapper doesn't seem to work properly. I'm honestly pretty confused about it. If I revisit and come up with a working solution I'll post an additional update. Next I'm going to test out multilevel which is what they recommend in the levelup docs.
UPDATE 2 8/15/2013:
Published August 12, 2013