http://blogs.adobe.com/crawlspace/2011/05/how-to-tune-photoshop-cs5-for-peak-performance.html
Keep in mind that bigger Cache Tile Size makes Photoshop *very* memory hungry...
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For Windows users:
Puran Defrag is free and very efficient http://www.puransoftware.com/Puran-Defrag.html
To know what is being loaded http://technet.microsoft.com/en-us/sysinternals/bb963902
To know what is running http://technet.microsoft.com/en-us/sysinternals/bb896653
Windows Tweak guides http://www.tweakguides.com/TGTC.html