Well, it seemed to me that applications on 10.5 seemed to be getting slower and slower to open. I looked around and found this application that helped things out.
XSlimmer, a $20-25 utility, "slims" your apps by removing the parts that you don't need. For me, since I have an Intel Mac and speak English, it removed the PPC components and all languages except English.

Photoshop is very fast to open now!

Also, if your Internet connection seems slow, try OpenDNS.