How good? Very great potential, but still in beta. Major effort is being put into security. There is a new Security Center in the Control Panel and on startup; it detects your firewall, AV, and update status allowing you to change or remedy first. The new firewall locks the computer down on startup; it's good, but I still use a third party firewall which the Windows firewall is built to support running two firewalls without conflicts. IE has improved security against certain viral-like activities and will not even load unsigned and uncertified scripts. Outlook Express still sucks, but what's news about that? Improved pop-up blocking in IE and the alert box for installing has three, or more, choices: yes, no, never, and, sometimes, just this once. All kinds of unseen changes in the registry to close security loopholes like the DCOM problem, etc. My guess is that non-tech users are going to be a bit befuddled why certain things don't work like they used to, and will either live with it or hire a tech support guy, like me, to fix the "appliance." You might want to see Thurrot's review at http://www.winsupersite.com/reviews/windowsxp_sp2_preview2.asp which is fairly accurate.
~SDC~