UCLA's Jeff Lewis has been keeping the numbers on Senate votes so far this session. In a helpful graph posted by Simon Jackman, we see that Democrat Arlen Specter is well to the left of Republican Arlen Specter, although with only 14 votes to the former's name, the standard error is a bit wide as yet.
Also of interest: Michael Bennet (D-CO) has been maintaining a relatively moderate voting record for a Democrat, sandwiched between Conrad and Carper. He's a few slots to the right of Udall, which seems like smart positioning for next year, as long as he can keep the base happy enough to avoid a primary fight.
Finally, as John Sides notes, Keith Krehbiel has predicted that Specter would not change his voting record as a result of his party change, while Nolan McCarty predicted the opposite. Color me shocked.