I think it would be pretty simple and basically the same principle as for Rails. You could just have several machines with Passenger (or whatever) running your

I think it would be pretty simple and basically the same principle as for Rails. You could just have several machines with Passenger (or whatever) running your app on each and stick a load balancer in front of them. (Disclaimer: I've never actually scaled things, but it sounds like that's more-or-less how it's done.) Really, the hard part almost always ends up being scaling your database. And since Sinatra isn't super-glued to ActiveRecord (though Rails3 fixes that), it would be easier to use whatever NoSQL-type thing you wanted if you got to the point of needing to operate on a huge scale.