Safari 'forgets' cookies, iTunes requires authentication 3 times?
My bet would be your keychain is corrupt. 

Launch Keychain Access in Applications/Utilities.

From the main Keychain Access menu choose Keychain First Aid.

Enter your password &amp; then Verify.

If it finds any errors, then run Repair.

I've found that after that, it can still find errors to fix, so keep running verify/repair until it runs clean.