It reports several problems with the update to the OS, and claims that we can expect more before the fix for the fixes is finally fixed.
One specific problem it cites relates to a change that SP4 has made to Relay Restrictions, meaning that web sites using IIS stopped having the rather useful ability to send mail.
You can find details and the Microsoft KB articles at the W2K web site.
But these are mere annoyances. If, instead you do a Microsoft KB search like this, you'll find 59 problems still to be fixed which may be considerably more irritating. µ