I agree with Eve. I've found Mark Warner an underwhelming, clunky speaker in the past; here's hoping he's honed his skills. He's also not an especially "new" face, though that may be more true from an insider's vantage than for the general public. (Also: Eve calls Warner "youthful," but he is 54, after all; this ain't 30-year-old Harold Ford in 2000.)
One thing's for sure: Obama has a reason to be grateful to Warner. There was very little talk of an Obama 2008 candidacy until Warner, who had been positioning himself as a formidable alternative to Hillary, abruptly decided not to run himself. Warner's exit, which freed up donors and media oxygen, was Obama's opening.
(I agree with the theory, by the way, that this suggests Tim Kaine will not be the veep, which would mean the media got pretty artfully played a couple of weeks ago.)
Last thought: Warner's "keynote" speech will be Tuesday night. Won't he almost surely be overwhelmed by the frenzy around Hillary Clinton, who also speaks Tuesday?
Update: Ambinder says Warner was approached for potential veep vetting, but refused.