Sometimes you forget just who the customer of a system is: We get so buried in the detail of what we are doing (and what we like to play with) that we forget the real world metrics that are applied.
The following is a video released by Yahoo! concerning how to optimise their web site. After the first few minutes it gets really techy (even I tuned it out about half way through) but the salutory point is made early: Traditional optimisation programs focussed on server and back-end performance (Yahoo are a web application after all); however, measurement show that the actual back end performance contributes 8-12% of the total time a user waits for a web page to display.
So performing a dynamite optimisation and halving your server time (which would take loads of effort and money) will result in a 4-6% reduction in the time it takes your web page to display. Or put another way, almost no noticeable reduction whatsoever.
So, the moral of the video: Remember that the system you are building is designed to deliver functionality to the user, not just get information from the back tier of your n-tier application to the n+1 tier.