Commentators and left-leaning Bloggers are breathlessly saying that McCain has given away the experience argument. 
But this seems too quick to me.  Think, for example, of Bush/Quayle vs. Dukakis/Bentsen. Bentsen did not save Dukakis's rear on the question of readiness to be Commander in Chief. Bentsen might have looked good in a tank, but that wouldn't have saved Dukakis's tail either. And Quayle's complete unreadiness did nothing to undermine Bush's standing as a former ambassador, former head of CIA, former Vice President. 

It's the same here, I would think.  It's the Democrats who have  got an inexperienced head of the ticket and a highly experienced VP.  The Republicans, on the other hand,  have got a highly experienced head of the ticket with a highly inexperienced VP. 
Why would Palin's inexperience  detract from the side by side comparison between the two heads of ticket? How can Biden's experience  compensate for that same comparison?

So don't count on McCain to surrender the experience argument at all -- no more than Bush the First did when he chose Dan Quayle or when Dukakis chose Bentsen.
Of course, there is the thing that Paul Begala pointed out -- but which I don't think either Obama or Biden can comfortably say -- that McCain is old and my even die in office.   That does make for  a disanalogy between Bush/Quayle vs.  Dukakis/Bentsen and Obama/Biden vs McCain/Palin.    But it would be pretty hard to exploit that disanalogy without seeming morbid and/or  ageist.   Wouldn't it? 
I think we're left with the question of what this choice says about McCain's judgment.   His argument would, I'm guessing, be that it shows that he is willing to make bold decisions in order to shake up the system.  He wants a fresh face to be his partner in remaking Washington.   Of course,  the fresh face is going to be relatively inexperienced in the ways of Washington.  But that doesn't detract from HIS experience in the ways of Washington.  She is the Junior partner, after all.  Not the senior partner. 
Obama himself made a parallel argument in his speech last night, though only in passing.   He admitted that his "career has not been spent in the halls of Washington" or something like that.  And he tried to turn that into a virtue. 
Well, it seems to me the case for that being a virtue in the junior partner of the team is much stronger than the case for that being a virtue in the senior partner of the team.