Why to write: Silflay Hraka has a cool piece on why to blog, basically arguing that the best thing a noncombatant can do in this war is fight with ideas. This is very true: from home we can't fight terrorism, unless we happen to be lucky and catch someone trying to shoot up an airport and be able to intervene, but we can help sway those who might give terrorists aid by using the power of ideas. A lone blogger won't have much effect, but the collective action of many of us will generate the ideas to convince the "Arab street" to support freedom, not oppression and get those ideas into the mainstream media where they can be heard. All of this is said much better in the linked article.
And another cool thing about it: the phrase silflay hraka comes from Watership Down, a novel expostulating about hero-journeys masquerading as a story about rabbits. Read it.