QUOTE(Raptor X7 @ Aug 7 2007, 05:23 AM)

I don't want to know how large they might be now.

Well, at any rate there's been no evidence that any larger nuclear weapons have been developed, in terms of either physical size or explosive yield. A bomb the size of the Tsar was simply impractical and in many people's opinion just a Soviet scare tactic. The Tupolev Tu-95 used to drop the bomb is absolutely mammoth, comparable to the B-52, and even then the bomb had to hang halfway out of the bomb bay.
As was mentioned in the OP video, the focus of nuclear weapons has shifted to missiles, and even though the nuclear warheads on modern American ICBMs may not have yields anywhere near the Tsar, they'd simply be much more useful from a tactical standpoint, being able to destroy enemy country's missile silos, airstrips, military bases, and cities in very short order, effectively neutralizing or at the very least crippling the unlucky country that got hit. There was a great article in Atlantic magazine a month or two ago about the fears people have over China's nuclear IRBMs when the reality is the USA could destroy their silos and render them harmless within a matter of minutes if the Americans decided to strike first to avert an attack on Taiwan.
I see a lot of people talking about how scary this thing is, when the fact is, the nuclear weapons of today are much more frightening, namely since if you pissed off the wrong person they could send one down right through your roof from halfway around the world.