I may be wrong of course, but somehow I don't think that these bomb threats are the work of kids. As far as I remember the two Olympic threats were made to Greek media and from the posts above, I'm not clear where the Virgin threat ended up.
Maybe the bad guys are just trying to test our resolve with the cry wolf principle, as someone pointed out earlier, and then when we become lax, whamo! Maybe the suicide bombers are finding it more difficult to get aboard?
In the early 80s I worked in a high office building which was evacuated 13 times because of bomb threats from the Puerto Rican Liberation movement. After the fifth time many of us decided to stay behind at our desks instead of walking down 24 floors and mingle on a cold sidewalk for hours until the cops said it was OK to go back in. You start developing a feeling of fate.
For history purposes, bomb threats and bombs on commercial aircraft started in the U.S. in the l950s when I believe some sick soul bought a million dollar, or something like that, insurance policy for his mother or wife. The plane did blow up but he was caught. However, ever since then, copycats, terrorists, disgruntled emplyees and others with an axe to grind toward a particular airline have used this method.
Some have been very successful, so don't let up on the possibility that it can't be me.