[eluser]toopay[/eluser]
Since Nick started talked about "Scalable-App", then someone(include Nick) maybe need to ask a simpe question : What (the heck) is scalability? And before (if we intend to disscuss it here) we go into the detail, we should dispel some of the falsehoods so common in contemporary web development literature by talking about what scalability isn't.
Scalability IS NOT raw speed. Performance and scalability are quite separate issues. You can easily have a high-performance system that doesn't scale, although the reverse is not often true-if system can scale, you can usually increase performance by scaling it out. Just because a system is blindingly fast for 1000 users and 1 GB of data, it's not scalable unless it can maintain that speed for 10 times the data with 10 times as many users.
Scalability IS ALSO NOT about using particular technology, including particular framework! In fact, scalability isn't about using any particular technology at all! So, wheter it is CI, Kohana, Symfony, Doctrine, FuelPHP or any "uh-oh" framework, a system built in any framework (even any languange) using any tools can be made to scale, altough the relative difficulty is an issue, of course.
