The Foiled Plots:
Like a lot of people, I've been spending a lot of time this morning trying to piece together what we know about the foiled plots to hijack and blow up planes bound for the U.S. from the UK. This report seems to be the most detailed so far:
More than 20 suspected terrorists were arrested in England by early Thursday morning, in an operation that involved British intelligence, Scotland Yard and assistance by a number of other law enforcement and intelligence agencies, including those in Pakistan.

ABC News has learned that two "significant arrests" in Pakistan in recent days may have significantly accelerated the pace of the investigation.

Many of the alleged terror plotters appeared to be of Pakistani descent. It appears that they were probably "homegrown" terrorists with strong links to al Qaeda and Pakistani operatives. This new generation of terrorists have figured significantly in plots in the U.S., London and Canada in recent months.

In this case, the plotters apparently intended to assemble small but powerful bombs in flight and use them to take down flights from England to the United States. * * *

According to a Department of Homeland Security briefing to the aviation sector, the terrorists appear to have planned to use multiple persons aboard each flight to assemble peroxide-based liquid or gel high explosives. The bomb-making materials could easily be concealed in small containers -- water bottles, tooth paste tubes, juice boxes and any of the other numerous person items passengers traditionally take into the passenger compartment of commercial flights.

At least nine transcontinental flights from American, United and Continental airlines were targeted in the plot. ABC News has learned that terrorists planned to attack the planes three at a time, waiting an hour between each attack.

According to federal authorities, two or three bombers would each carry a separate portion of the bomb onto the plane to avoid detection. Once onboard the bomb would be assembled and then detonated by using heat or friction.

British authorities had been tracking some of the suspects for several weeks but stepped in to round up the plotters when they began to book flight reservations.
It's always hard to know what to make of stories of foiled plots, but this one sure sounds like a biggie. It sounds like the group was being tracked for a while, too, and (I would assume) pretty comprehensively; if investigators knew that the plotters "began to book flight reservations," and had a sense of the particular flights at risk, it seems safe to assume that at least a portion of the overall group was identified and UK investigators were tapping their phone/Internet connections. But of course it's hard to tell from the outside, especially just from early reports like this, and it's unclear when (if ever) we'll know the real details.