Go here for reactions to the speech by foreign leaders.

Here are some domestic reactions (via Sully):

Yglesias:

This is a guy who’s not afraid to try to express complicated or difficult ideas…his whole team is clearly imbued with the same spirit and that same mandate to try to really explain the complicated and difficult ideas rather than sweep them under the rug. This seems connected to me to the remarkable way in which this speech is being pushed out in multiple media—on television, but also on Twitter and on Facebook and via SMS and all in multiple languages—to a global audience. Part of the rise of Obama is the rise of a post-television, post-sound bite technological paradigm. You can deliver a speech at 7 AM Eastern Time and know that even though relatively few Americans will be up to see it, anyone who’s interested will be able to Google up a transcript…It creates a whole new world from one in which the point of a speech is just to field test a couple of zingers in hopes that one or two of them gets picked up for the evening news.

Fallows:

This was yet another in the series of speeches that individually and as a group really are out of phase with anything we have known in contemporary political rhetoric. I mean a sequence that began most noticeably with the “race and America” speech in Philadelphia 15 months ago and has continued with five or six clear high points since then (most recently at Notre Dame, as discussed here) and no obvious flop.

The Economist:

[T]he constant refrain, heard on Cairo’s streets as well as from media pundits, is that Arabs and Muslims would like to see Mr Obama’s words matched by deeds. “To win our hearts, you must win our minds first, and our minds are set on the protection of our interests,” declared one of the reams of editorials, columns and open letters from across the region.

Alex Massie:

[A]s the President said, a speech is just a speech. But that doesn’t mean it is only a speech. Obama’s ambition was to speak to Muslims all around the world, not just to dictators and princes and emirs. The existence of the speech was probably more important than anything Obama actually said – most of which will be just as perishable as most speeches. But the image of th American president in Cairo may endure rather longer. Who knows how much it can achieve?

Update: And this from Gherald:

The Cairo speech is majestic. We cannot know how effective mere a speech will be–much depends on the execution and willingness of the parties involved. But I’m sure it will be positive, at least at the margins (i.e. help to dampen extremism)

Think back for a moment to over a year ago, before the financial crisis. This was the principal reason for Obama’s candidacy, especially during the primary. No one is in a better position to promote peace.