When do you tune your apps?
I like
EricGu's article on when to do performance tuning. I agree with some of the remarks particularly about the "intution based performance tuning". I have bitten once too many times by premature optimization and speculative optimization.
I try to get the performance use cases early in the design process so that its an active player in the development. But, Its importance is lost to many that it is as important a requirement as a functional use case. I think it requires a certain discipline to design for modifications to accomodate performance issues as discovered. I think the new tools seem to (unfortunately) make it all to easy to design a beautiful, perfectly functional application that cannot scale beyond 10 concurrent users.