A key part of algorithm selection is having a realistic benchmark or workload in hand to support making decisions based on actual results rather than intuition or folklore. This means the most effective time to do performance and scalability work is in the earlier phases of the project, perhaps the exact opposite of what usually happens. All the clever compilation options are pretty useless when dealing with O(n2) algorithms for large values of n. Poor algorithms are the number 1 (and probably numbers 2 and 3 as well) cause of poor software system performance

-- Bart Smaalders, Performance AntiPatterns, ACM Queue, Vol. 4, No. 1 - February 2006