No problems with Safari on Mountain Lion here.
If installed, try temporarily disabling anti virus software.
Check Safari > Preferences > Extensions. Turn that off if there are any installed, quit and relaunch Safari to test.
Deselect: Enable plug ins in Safari > Preferences > Security
Quit and relaunch Safari. If that helped, follow the instructions for troubleshooting third party plugins here.
Delete the cache and cookies.
From the Safari menu bar click Safari > Reset Safari
Select: Clear History (also empties the cache)
Deselect the remaining boxes then click Reset
Back to the menu bar, click Safari > Preferences > Privacy
Click: Remove All Website Data (removes cookies)
Quit and relaunch Safari to test.