"This will certainly give a boost to al-Qaida morale, because being able to attack a large superpower with coordinated attacks during a summit meeting when security and targets are even more hardened is a sign of success.
Rather than attacking during the Live8 concert series, whose members terrorists would want just as dead, the attack fell during the G8, which has an important effect on those on the far left.
In other words, rather than alienating the important part of the public that gives terrorist sympathies (meaning those who will claim they are merely freedom fighters), terrorists have "protested" the same entity as them---G8 summit.
And of course, not all Live8 participants are of the far left and have sympathies with terrorist groups, but surely there are a number.
Now this will also force questions if London can handle the security needed for the Olympic games."
http://www.terrorismunveiled.com/athena/2005/07/terrorist_attac.html