I am using it on a small production environment with Heroku and I like it, but when we officially launch the app, should we switch to Unicorn?
This seems to be missing from most of these project sites, which are often just marketing (look! It's better!!), and therefore not very trustworthy.
From the outside it looks like the biggest differentiator in each generation of ruby servers (and, I guess, db managment systems :) is not that the new is better or worse, but simply that has different trade-offs.
Although as noted in the comments, I neglected to run threadsafe! and should have probably tried rubinius or jruby. I have been meaning to redo. Take with a grain of salt
Overall really solid, though more useful if you can use something other than MRI.