Performance is perspective that all the developers forget during development and it pops up and the end of project (worst time). for SharePoint development there are a lot of areas to tune the performance (Code, caching, farm network design..etc)
Below a set of good white papers and posts which puts in on a track for performance optimizations:
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[Update] Top SharePoint Storage Resources
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[Update - 2/11/2008] How to Optimize a SharePoint Server 2007 Web Content Management Site for Performance
ciao