The failure to stop Nigerian Islamic terrorist Umar Farouk Abdulmutallab, before he could attempt to blow up an airliner on Christmas Day, has caused a media uproar over the failure of the American counter-terrorism system. Various intel agencies have released, or leaked, details of who knew what and when about Abdulmutallab. He was turned in by his father, to the American embassy in Nigeria, a month before the attempted bombing. As a result, Abdulmutallab was placed on a "persons of interest" list, along with another half million people. Abdulmutallab was not placed on the "no-fly" list, nor did anyone check to see if he had a visa to enter the country (which he did.)
The CIA had been collecting information on al Qaeda in Yemen, and knew that someone named, "the Nigerian" was being prepared for a mission. There was also some chatter about an attack during late December. The intel agencies have been accused of "not connecting the dots" and catching Abdulmutallab before he got on that plane to Detroit.
There are some institutional reasons for the failure to effectively analyze all this data and catch Abdulmutallab earlier. First of all, there are many similar patterns of potential terror attacks than the public never hears about. The counter-terror agencies have limited resources, and they cannot put a lot of effort into every potential attack. Then there is the personnel quality problem. The government has to compete with corporations for people, even in the area of intelligence gathering and analysis. The corporations tend to get the best people. But worst of all, the people who run the many counter-terror organizations, and subdivisions thereof, are either political appointees (selected more for loyalty to the boss, than administrative or counter-terrorism skills) or civil servants (those who were not hired away by corporations, and rose through the ranks, usually because they kept their heads down and didn't make waves.) While there are some extraordinary people in the government counter-terror bureaucracy, they are the exception, not the rule.
Then there is the reluctance of intelligence agencies to share information, lest another organization's sloppy security reveal "sources and methods" to the enemy (usually via the mass media, always eager for a hot headline.) Given the small number of actual terrorist attack attempts, the intel agencies are more concerned with protecting their sources (often very vulnerable people, very close to the terrorists) and methods (how they eavesdrop on enemy communications, or recruit informants).
Finally, let us not forget that something similar happened with the 19 Moslem men who carried out the September 11, 2001 attacks. After numerous investigations, it was found that there were diligent and alert personnel who detected these killers, but they were outnumbered and overwhelmed by political and civil service hacks who were not on the ball. So remember that, after the dust settles on the Abdulmutallab screw-up, the organizational culture that created it will very likely not change. And it will happen again. Happy New Year.