From a reader: I believe there is some confusion over what the court actually said. They did NOT say it was ok to enter without knocking. In fact, the parties conceded as a given that the entry in this case was improper.
The discussion and the decision were entirely about whether the EXCLUSIONARY RULE applies in this case, and a majority decided that it did not. In other words, valuable and otherwise valid evidence of guilt could still be presented to the jury. The plurality decision pondered whether the exclusionary rule, adopted in the early 60′s, was still necessary at all, pointing out that there are other remedies available to both serve as deterrents to police misuse of authority and remedy existing violations, such as federal 1983 civil rights actions and civilian oversight of police.
Excluding evidence of guilt is, after all, a pretty draconian solution when you think about it. The Warren Court felt that it was the only way to control the police. This court is starting to think that maybe it isn’t.
On the facts of this case, I think that the existence of an actual warrant for the items seized is what brought Kennedy over. The others (i.e. The Good Guys) look plenty ready to declare the Mapp Rule an idea whose time has passed.

And from another reader:

Jonah,
My father and brother are cops, and I’m joining the Air Force JAG, so you
know where I’m coming from.
I see nothing strange or inappropriate in the Court’s ruling, and some of
the press has been misleading about how narrow and sensible this ruling
really was. The Court did not say cops don’t have to knock and announce
their presence. It did not even say that they should but won’t be punished
for failing to do so. Rather, the Court wisely stopped from further
expanding the exclusion doctrine that the defendant sought. The cops have a
warrant to go in the house, they knock and announce, but they don’t wait
long enough (what is “long enough?” Nobody really knows) before going in.
And this guy wants all the evidence suppressed. They had a warrant to enter
and search for guns and drugs; they did enter and search for guns and drugs;
they found drugs and guns. There’s no doubt they could have waited a few
more seconds before kicking the door in. But because they were just a
little too impatient, the whole case should vanish because the defendant
couldn’t get to the door fast enough? Remember, we’re not talking about a
warrantless search here. The cops had every right to be there and every
right to search. There’s no call for suppressing that evidence on some
vague standard of “how many seconds” do police have to wait before going in
to execute a completely legal and by the book search.
As it is, the Court in 1995 unanimously ruled that the knock and announce
rule was constitutionally mandated as well as a sensible means of preventing
accidents. So that’s not going away. The only question was what the
consequences will be for failing to do it properly. Throwing out the entire
case on a hard to measure technicality, or allowing innocent victims to sue
officers or police departments for proven knock and announce violations? I
think the Court wisely chose the latter as a way to maintain incentives for
knock and announce without jeopardizing otherwise entirely legal searches on
how fast you can count to 5-mississippi in the heat of the moment.