I've seen that article before, and thought it was remarkable in its lack of substance.
I find it hard to blame Obama for not breaking with his party while in the Senate when there has been so little reason to do so over the past three years. If the author of the article had some specific issues where Obama should have voted the other way, he should bring them up. Otherwise, the allegation is an empty one, relying on form over substance. One or two examples does not constitute a trend.
Moreover, I'm tired of the charge that he is the most liberal member of the Senate. Again, if there are issues on which he is far-left, they should be named and discussed. But he and Clinton had similar positions on just about every major policy issue, so if she isn't left-wing, then he can't be left-wing either. Their biggest difference was on a mandate for individual health insurance, and Obama had the more centrist view on that one.
If people like McCain's positions more than Obama's, by all means they should vote for McCain. But I wouldn't pay much attention to screeds that paint such a one-sided picture.
And shall I go into all the ways McCain has conformed to his own party's dictates over the past few years? I think he's got a bigger gap between what he said and what he does than Obama. Not that what McCain had said or done in the past would matter to me if I thought he had moved to better positions--but in my opinion when he's shifted he's moved the wrong way.