I also think the chances for a national ID card here also took a massive leap upward. London is one of the most surveilled cities in the world, and still the killers managed to do this. People over here will be saying we need to do more, and "obviously" knowing who's legal and illegal would help. (Ignore McVeigh, Padilla, John Walker Lindh...) So I think the chances are much better now. I'm not for a national ID myself - I mean, we've seen how badly credit companies handle personal info; just imagine how badly the government would be at it. (Post on this to follow)
Initial guess - it is Islamists, most likely al-Qaeda linked. (Not too hard to believe, since offhand I can think of only a few Islamist groups who aren't al-Qaeda linked and who operate outside the Middle East now, a la Hamas and Hezbollah.) While I've seen some commentators say this attack was "less effective" than their previous efforts, 9/11 and 3/11, I'm not so sure. The deaths were less, yes - but look at the effects of shutting down the transportation system to the extent they did, and also the fact the authorities shut down the cell phone network as well. If they only killed one person, but that resulted in a massive shutdown of some critical network, I'd say that's kinda bad overall.
It looks likely it's suicide bombers as well, since as Andrew Sullivan pointed out cell phones wouldn't have worked in the tunnels. Remotes are also possible, but I would hope that any unattached luggage would have been noted and responded to.
Here's a scary thought - what if it comes out that the bombers were people who had fought in Iraq and learned their skill there? Kinda takes the wind out of the argument "Fighting them over there so we won't fight them over here", doesn't it? (never have liked that argument - does this mean the entire war was so we could use soldiers as bait? Ugly, nasty thought...)
I wonder how soon it will be before nuts on both sides start tossing off the crap - "It was a setup to take the heat off Rove and Bush!" and "See, liberal wimps, you're to blame!" Can't we set up a web site where these morons can go and flame away at each other and leave intelligent people to debate? And then delete it and all the people in it? (Update: not long at all. Here's some madness from the conservatives (via Demagogue) and here's some from the liberals (via snarkbait).