If your Safari is slow to start up, one thing you can try which may fix this is deleting the plist file. To delete it, open the finder and go to the root directory for your user. Then change into the Library directory, and then change into Preferences. Delete the file called com.apple.Safari.plist in this directory.

When I did this, I got much quicker launches of Safari afterwards. One important point though... deleting this file may remove some of your preferences that you have set. If this happens, you can just reset them in Safari.