Time to put Zawahiri's appearance into context. His last appearance in June is likely linked to the bombings in Sharm el Sheik (Egypt). I make this linkage due to the threats against Egypt and Saudi Arabia made in that video. I suspect that the July London 7/7 bombings and later attempts could also be linked.
This new video threatens Britain (specifically) and our European allies (in general). What concerns me is the threat of 10's of thousands of American causalities in Iraq/Afghanistan and the comments about NYC and D.C. I don't think they are capable of inflicting those causalities in Iraq/Afghanistan. However, the potential for here exists. Is this a nuclear threat? I'm still not convinced. Subway bombings in Europe have sent chills down the spines of Americans here. A coordinated series of attacks across the country would have a significant effect upon the American psyche, with no need to use nuclear.
If Iran is in bed with AQ leadership, the last thing they'd want would be a nuclear terror strike on mainland US. That would give GWB more than enough reason to level Iranian nuclear facilities and send them back to the stone age.
Regarding Fullwaves's photos. Here is a quick summary of activity associated with Zawahiri's videos:
May 03 - Two weeks later German forces were attacked in Kabu (4 died)
2004 (general)- Multiple attacks follow his videos including Madrid, coordinated nationwide Iraqi insurgent attacks, and attacks on Israeli Red Sea resorts.
Feb 05 - No associated significant attacks.
June 05 - Egyptian (Red Sea resorts) and possibly London
My gut feeling is that Europe has a high probability of an attack. Most likely Italy, followed by Britain and even possibly Poland. I'm not sure about the US, but if they still feel our mass transit is vulnerable, inspite of what was learned from London, that would be a prime target and dramatically increase our potential for attack.