I'd suggest you try the following as it's proved very beneficial for me:
1) Use Xslimmer, as it reduces the program to only its Intel binaries. Since Leopard has to see which one's to use, having only the Intel ones not only removes the hassle but also saves a ton of space.
2) Some may have different opinions about this, but iDefrag proved quite useful. Burning a boot DVD with CDMaker and defragging the hard drive, I noticed shorter times in bootup, shut down and even loading of apps.
Permission repairs also play a role but the above are supplements as well.
Hope this helps!