Safari got off to a great start, but it's not living up to its promise. (A bit of a trend with some of Apple's software; iCal, iPhoto and maybe iSight are other well known examples.) Apple seems to be in a trend of great beginnings with a failure to follow through. This wouldn't be so bad, except Apple's great beginnings are knocking all competitors off the Mac platform.
If Apple is going to be the dominant Mac OS X application vendor, they need to fix their products faster. Maybe a widely available "beta" program?
Apple - Discussions - Safari slowdowns: quick & easy fix
My Safari 1.0 suddenly became very slow to launch, and started giving beachballs a lot... The fix I finally found is easy--and several other people have said it works for them too. You could try it even if you don't know you have a problem--I've been told it has helped people who didn't even know Safari could be faster.
Empty out the Icons folder in your user's Library/Safari folder. (I left the folder there, but threw out what was inside.)
Start Safari up and all should be well. No need to throw out prefs, Reset, repair permissions, or re-install Safari. I've heard some very painful fixes for this problem--and they usually include throwing out a lot more than necessary.
The culprit seems to be a bug regarding the favicons (the little icons on bookmarks). That Icons folder stores the favicons of the places you've visited. It can grow to several MB--but whether that's what triggers the bug I cannot say.
Side-effect: After doing this, your bookmarks will have generic icons. But don't worry, as you visit your bookmarks, each icon will return. Use this tip at your own risk, but it seems pretty harmless.