Seems to be working all right. One nice touch: it runs Rails apps as the user who owns them. So it should work very nicely on shared hosting, which often suffers from the problem that making everything visible to the web server also means everyone can read everyone else's database passwords.
I wonder if it's possible to configure it to run in pure-forking mode, i.e. so that Apache+Passenger starts up and boots a copy of each Rails app, then on each request, it forks a child process, which processes the request then exits. It's uncommon for servers to run that way as it kills performance, but it's great for memory usage, so should work much better on memory-limited servers (like my old dedicated box and Slicehost VPS, with 256M each), especially if you want to run several Rails apps (which I'd of course like to do).