On one level the whole thing is part of the silly kind of politics that Obama is trying to move beyond, but on another level it's important because until and unless Obama can give as good as he gets in this sort of thing there's no chance of moving beyond it.
So long as the Republicans think that negative crap works, they will keep doing it. It's a lot easier than actually debating the merits of things, after all. Obama will actually be doing the GOP a favor if he can de-fang the crap-style politics enough that they decide to return to actual issues. (There will never be a complete end to negative campaigning -- it's like Evil, you can't permanently defeat it.)
Conservatives actually do have many valid points on many issues. Unfortunately, under Bush, the conservative movement and the GOP generally have, in the immortal words of Charles Barkley "lost their minds."
Until they return to actually trying to beat liberals with real arguments, they will come out on the short end of things. Because, at the end of the day, being as ass is not enough to win arguments with people.
So, does it really matter that McCain doesn't know how many houses he has?No. But then it didn't really matter that Obama wasn't a big fan of flag pins, either.
But trying to paint Obama as some sort of elitist is not the place the McCains want to go. Obama got into Harvard on his own merits, made his own money, grew up raised by a single mom, etc. McCain, meanwhile, got into Annapolis as the son and grandson of admirals, married wealth, etc. Should it be held against McCain that he's rich? No, but it's also not a reason to vote for him.