Many readers like the idea. A typical email:
Makes a ton of sense, subject to the caveat (is he a loose cannon?) that you noted. He reinforces Obama's "Iraq" and "change" messages; has national security cred (was Reagan's Navy Secretary) without being an old insider; clearly has the testicular fortitude to be an attack-dog when necessary, yet (as a former Republican) can claim to be post-partisan; has (had?) a son in Iraq just like McCain; was a Vietnam hero like McCain; and may even be able to reach the Appalachian Scots-Irish demographic that Obama has had so much trouble winning. And, of course, he could help in Virginia, a state that already looks promising for Obama.