Ross Douthat makes some smart points about the merits of Webb as veep:
[T]he beauty of the Webb pick is that it has the potential to offer the best of both worlds. Yes, it addresses some of Obama's weaknesses (national security, the white working class) and maybe helps him in the potential swing state of Virginia. But it also doubles down on one of his biggest strengths - specifically, the notion that he's the standard-bearer for a post-partisan Democratic Party. After all, what separates Webb from, say, a John Kerry or a John Edwards - both of whom appealed to Democrats because they seemed to (but didn't really) shore up the party's weaknesses on national security and with the white and Southern working class - is that he really is a different kind of Democrat. He isn't a conventional left-liberal who happens to have a military record and/or a Southern accent; he's a more sui generis figure, a cultural (though not social) conservative with heterodox views on a variety of issues.
This is why, were I Obama, I would look at the left-liberal case against Webb - on the grounds that he's too anti-feminist, too pro-military, too skeptical about affirmative action and immigration, too hostile to Hollywood and academia - as an advertisement for the pick. An Obama-Webb ticket wouldn't send just a message that people who share the same ethno-cultural identity as Jim Webb can have a home in the Democratic Party, the way Kerry and Edwards were supposed to show that veterans and Southerners could too be Democrats; it would send a message that people with Webb's views can have a home in the party.
The only caveat I'd add to all of this is that I think some parts of the left-liberal case against Webb are more consequential than others--namely his views on women. It's a pretty safe bet that the women who are hurt and angry about Hillary's defeat will, facing a choice between McCain and Obama, go with Obama. But I think Obama's picking Webb as his runningmate could complicate that--since some women would view it as a slap in Hillary's face. Unless, of course, Obama made it known that he offered the job to Hillary first and she turned it down--and, maybe even for the sake of drama, recommended Webb as the better choice. (Hey, it doesn't have to be true! The various players just need to say it is!) In other words, if Obama does choose Webb, the choreography of the choice may be as important as the choice itself.