Profiled performance does not equal real-life performance.

Ian nails it* with this post to the DevelopMentor Dotnet-CX mailing list. Profiling does not give you a real view of the performance of a segment of code, nor does the performance of a segment of code reflect the performance of that code in real use. Don't optimize the performance of something unless you:

• Have a reproducible test-jig for repeatable performance testing
• Have an idea of the baseline performance
• Know where the bottlenecks really are in the code
• Can tell if the performance of the system gets better or worse with changes.
• Have an idea of what performance is good enough

* apologies to Don Box. Edit: Ian blogged it here.