Over at TNR Eve Fairbanks and Jonathan Cohn argue the question.

My two cents on the subject are that while Romney might bring some economic heft to the ticket his drawbacks are pretty substantial. First among them, Democrats would have a fine time ripping Romney for his flip-flops just as his Republican contenders did in the primaries. Not a big deal? Perhaps not, but when one thinks about all the reasons Romney should have been the nominee, his failure can be attributed to his inability to pander well. Republicans just didn't think he was genuine. Polish does have its drawbacks.

Romney is a good debater, however, and we might be thinking too much about his qualities as a presidential candidate as opposed to a vice presidential candidate. After the initial buzz of the running mate announcement, a VP pick's really only other responsibility on the trail is the single VP debate. Up against someone like Joe Biden, Romney could handle himself. Also, while voters might think Romney can't pander worth a darn, they probably can see him as an effective executive.

So it is a wash? Well, as Cohn points out in his case for him above, McCain doesn't like Romney (or so the cw says). That could tip the balance against him.