I'm firmly in the "He's a panderer" category. He knows which way the wind blows, which is why he often sounds like he's going to help our side. But he also knew that doing so would hurt him in the Republican primary, so he couldn't help us much. But now, he doesn't have a Republican primary. So now the political winds are pushing only to the left, which is what he'll do. Not that he'll be the most liberal member of Congress. But he'll have little incentive to side with Republicans.
Of course, to make this work properly, he still needs to worry about a Democratic primary. And so if they somehow promised him full support no matter what he does, that'd be a huge mistake. Because then he'd have every reason to side with Republicans. But I can't imagine they'd have been that stupid and would have made it clear that they expect him to vote like a Democrat if he wants Democratic support. And in any case, bloggers like Kos and Atrios have enough power to cause him some amount of grief in a Dem primary; and so it'd behoove him to not take the Dem primary for granted. At least not for his first one.
And so overall, I think we're going to see a different Arlon Specter. I think Arlon is looking out for Arlon and that means he's going to be siding with us. Not that he'll take the lead on much or give as much support as we'd like, but I predict that he'll be a much better Democrat now that he's a Democrat.
Update: For all those interested, I'd like to point your attention to Donald Douglas, a conservative blogger who wrote 171 words to laugh at me for misspelling Arlen Specter's name in this post; as well as an additional 88 words in a comment he left here. He suggests that the name "Arlon" might be Klingon, even though it's a real name. In fact, I know someone named Arlon, whose name I type and read regularly, which was probably the source of my confusion.
But if anyone's looking for answers on why the conservative blogosphere is failing to keep up with the liberal side, bloggers like Douglas are a good place to look. They really don't give a damn about conservativism or liberalism, they just hate liberals.