Maybe someone can share from his experience about developing an application that is meant to scale big time where just throwing more money at better hardware isn't a realistic option using development methodologies such as SCRUM and XP.Did you need to rewrite substantial parts of your app because of current framework couldn't scale enough to fit current sprint'sstories? how do you avoid that?   When do you do stress (or load) testing?  In what stage did you make your SMART(TM) design concerning bleeding edge requirements?  Did you add more stages to the dev-cycle of write-a-test, code-to-pass-test, refactor?  Did you just refactor everything in the end to meet demands?  
Developing scalable applications using Agile methods
agile;scrum;scalability;extreme programming