For read only file systems there is a specific config.hobo.read_only_file_system heroku-aware (i.e. it is automatically set to true when the app is started on heroku), that you can also explicitly set in your application.rb or <environment>.rb, that will prevent generation of dryml taglibs and auto generated routes.
Besides the setup_wizard will ask you whether you want git to ignore the auto generated taglibs and routes, because having them checked in will avoid you a manual deploy in heroku apps, so it may be preferred.
ciao
dd
sounds good though is there a method in place for read only filesystems, ala heroku?