I've seen a bit of discussion around the few left-wing blogs I still read in which folks offer predictions as to if, and therefore when, a Republican Congress will impeach President Obama. So, my take is this: it won't happen in 2011 or in 2012, simply because if the Republicans take Congress this year, they -- and the media that crowns every political development in the United States as great news for Republicans and further evidence for the notion that the US is a "center-right nation" -- will see President Obama as mortally wounded, and they will bank on being able to easily beat him in 2012.
Now, if they're in control of Congress and President Obama wins a second term -- the latter of which still seems fairly likely to me -- then I think the probability of a Republican charge to impeachment on some kind of weird grounds is almost a certainty. Why? Because having a Democrat in the White House makes Republicans just insane.