Megan is against it:

Nixon fell because his behaviour was inarguably criminal, and worse, petty criminal. And he had it all on tape.

Bush's behaviour is not inarguably criminal. Impeaching him will generate a gigantic mess. And the negative feelings about that gigantic mess will almost certainly be laid at the Democratic Party's door. An impeachment is almost the only thing guaranteed to deliver a Republican president and the loss of at least one house of Congress in 2008.

But Cheney? Not sure the same caveats apply. Dave Weigel responds:

So an impeachment trial would 1) waste Congress's time, 2) take the Democrats' knees out, and 3) humiliate Bush and legions of wide-eyed Republicans. And... what are the arguments against it?