Good explanation of the differences between Passenger and something like Mongrel. To me, the ability to dynamically start and stop processes is what makes Passenger such a clear winner for what I do with it.
I know it's not planned (I asked them!), but for many small apps, it would be great to have a simple flag to tell Passenger "I need 1 worker (delayed_job, resque) for this app, please keep one alive", vs running monit or similar.
While I think that Passenger Lite might be useful for development, I would think twice about deploying my production app without a full blown web server, just for the sake of being able to run non-ruby code if needed.