Amateur?
1. Timed bomb attacks in the same area.
2. High-powered explosive device surrounded by low-budget shrapnel.
al Queda attempted other attacks with less success or lower degree of damage. al Queda doesn't have a high profile figure head, since he was deep 6'ed. They still exist and the anti-American extremist Muslims are still in the US.
I'm pretty disgusted by the overriding al Queda/Taliban sentiment here.
Time for more waterboarding.
aq's m.o. is usually more dramatic and devastating attacks. they go for higher profile targets and more kills. for example, look at the suicide bombings elsewhere across the world. they take out 20+ people at a time. not exactly something you get with an open air shrapnel bombing at a marathon. the timing of their bombs are also placed further apart in order to maximize causalities to first responders as well. if they wanted to maximize kills they easily could have placed this on a train, mall, airport terminal, etc.
sure they've had failures, but pretty much all of their failures were aimed at very high value targets and many kills. failed wtc bombing the first time and two failed airplane bombing attempts, for example. i also wouldn't consider this a failure since both bombs went off as planned.
considering the target and other circumstances, this just doesn't seem like an organized aq operation. it could be, but just doubtful...