The biggest play of the Super Bowl to me (pick one!) was James Harrison's one-hundred yard interception return at the end of the first-half. It was not just a pick-six, it was a pick-thirteen (with the ball so close to the end zone, Arizona's expected points was around six, and the resulting touchdown was obviously a seven point play).
Strategically it was also fascinating. The Steelers had been blitzing quite a bit, Warner thought it was a man-blitz, but instead Harrison dropped off into the passing lane. LeBeau has gotten a great deal of credit for this call, but at least some reports have been that Harrison was supposed to blitz but instead stepped back into the passing lane, after faking the rush.
In any event, though you can't tell the exact nature of the defense (defenses are always compressed near the goal line, and even if LeBeau did call it, it could be man with Harrison dropping off as a spy or "floater," or if it was a true zone-blitz. But it does bring out something I want to highlight with zone-blitzes: zone-blitzes do not solely occur when a defensive lineman drops off into coverage. Indeed, the entire point of the 3-4 is that you can use a zone-blitz scheme without having to drop off ends and tackles; you can just change up the linebackers who come. Quite literally, it is anytime a team employs a blitz with a zone coverage behind it. Most "fire" zones use the end dropping off, but it's not necessary.
Now, a common technique involves one often done by dropping defensive linemen, or by a player like Harrison: the step-up like a blitz and then drop-off. This technique is really independent of the scheme, but works well within it because it freezes blockers, thus making it more difficult to block the overload blitzes. This is how well-designed and executed zone-blitzes can get a free rusher with only five guys after the quarterback.
While it might seem more interesting to limit zone-blitzes to situations where a big lineman drops into coverage, it is not accurate. Indeed, they are still revolutionary because typically blitzes are forced into man coverage because, to get the advantage in rushers versus blockers, they only have enough guys to go man to man or maybe man with one help player (usually a deep safety). The zone-blitzes try for the best of both worlds with a simple coverage (three intermediate, three deep) and a five-man blitz. They try to be effective by being well disciplined at both: using a matchup-zone or pattern read approach with the coverage, and scheming the five rushers to take advantages of weaknesses in the coverage.
The good teams, like the Steelers, are dominant. But there's lots of bad zone-blitzing teams around. Zone-blitzing can sometimes be a bit like playing with fire.