How to turn back on "FTP://username:password@ftp.site.com" after installing sp2 ???

It is not possible because security reasons... This was quite often trick for creating false links, look at this link:

http://www.microsoft.com:updates@myevilsite.com

That was the reason why microsoft remove this functionality (it was before SP2 with one hotfix)

Add this to the Windows Registry

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_HTTP_USERNAME_PASSWORD_DISABLE]
"iexplore.exe"=dword:00000000
"explorer.exe"=dword:00000000

nice, thanks for that SuriBoiWA!

Thank you !