Glenn Reynolds has a roundup of reaction to the press conference; I listened to it on the radio (well, technically the XM Radio simulcast of Fox News Channel, so it was TV without the pictures), and I think it came off about as well as a Bush speech ever seems to, which is to say that the ideas were solid and the tone was right (as in the State of the Union), but W will never go down in history as a great public speaker.
Then again, I'm not sure that many politicians these days are. Clinton was a decent public speaker (at least by comparison to the Bushes, Ross Perot, and Bob Dole), and Reagan of course was a master; on the other side of the pond, Tony Blair and Margaret Thatcher have it, but John Major decidedly didn't. And, for all the talk of congressional oratory, most of the representatives and senators I hear these days can't talk their ways out of paper bags, although I recently had a chance to hear John Spratt (D-S.C.) in person, and he did a fairly good job. Clearly being a good speaker is not a requirement for political success — although sometimes it can help.
I do wonder at some level who the speech was really aimed at. Several of the comments at Glenn's suggest that it was primarily for foreign consumption, while some of the commentary I heard on FNC suggested it was more pointedly aimed at the U.N. My gut feeling is that the place it will have the most effect is in Britain: the nuance won't get lost in translation, so there's a limited opportunity for spin, particularly if it doesn't get sound-bited to death.
I'm not sure that in the end it much matters, though; Blix will give a report that everyone can take something away from, some sort of resolution will be presented in the form of an ultimatum which will probably pass, and there will either be an internal putsch or a war. In six weeks, Chirac and Putin will be scrambling to make sure they are on good terms with a new Iraqi government, while Schröder will be preoccupied with domestic concerns, namely trying desperately to keep the Greens in government.