Safari 5.1.2 is slow, pages need forced refresh

Question

In the past, I could have a large number of tabs, and Safari worked fine. Recently (I'm not sure how long agao this began), it's gotten slower and slower. Often, when I go back to a tab, it's completely blank. When I try to refresh the page, I get an alert saying that I need to force-reload all of the open tabs. It often takes a very long time.
Generally, the app runs unacceptably slowly a lot of the time. How can I fix this?

Answer 1

Please read this whole message before doing anything.
This procedure is a diagnostic test. It won’t solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.
The purpose of this exercise is to determine whether the problem is localized to your user account. Enable guest logins and log in as Guest. For instructions, launch the System Preferences application, select “Help” from the menu bar, and enter “Set up a guest account” (without the quotes) in the search box.
While logged in as Guest, you won’t have access to any of your personal files or settings. Applications will behave as if you were running them for the first time. Don’t be alarmed by this; it’s normal. If you need any passwords or other personal data in order to complete the test, memorize, print, or write them down before you begin.
As Guest, launch the application(s) and test. Same problem(s)?
After testing, log out of the guest account and, in your own account, disable it if you wish. Any files you created in the guest account will be deleted automatically when you log out of it.