Why haven't there been more terrorist attacks lately?

[Skyclad Lad]

Or any of note, for that matter...
If you believe the U.S. government's estimate that there are some 5,000 Al Qaeda members or A-Q sympathisers in the country (and I don't, but there are surely still a good many), why haven't they done a thing lately? Is the security in America really THAT good?

What, further, is the point of the Terrorism Alert-O-Meter, or whatver it's called? Wouldn't the terrorists simply wait until it had been dropped to a less severe level before striking, thus rendering it useless?

Please, guide yours truly, a humble Welshman, through these troubling waters with your opinions!