Nothing new, you say? No, I don't mean it in that sense.
As we get closer to the general election between Obama and McCain, there is whispered speculation about potential Cabinet appointments by the eventual winner. Here, for instance, is recent speculation in Roll Call, regarding Democratic possibilities.
If we were at a comparable point in a British election cycle, there would be more certainty in that regard. That is because the U.K. has an institution that has no direct American counterpart: the Shadow Cabinet.
That is a group of the opposition party's members of Parliament (either house), each of whom "shadows" a member of the governing party's Cabinet. That involves being the opposition party's spokesperson on the relevant issues. So, for instance, the shadow chancellor of the exchequer is his or her party's spokesperson on Treasury issues.
When an opposition party becomes the governing party, Shadow Cabinet members often take over the position that they had been shadowing. For example, when Labor won the 1997 general election, Gordon Brown, who had been shadow chancellor, became chancellor of the exchequer.
It's not automatic that a Shadow Cabinet member takes over in that manner, but the system is set up to prepare them to do so, and they often do.
The party leader of the largest opposition party is known as the Leader of Her Majesty's Loyal Opposition. That leader is, in effect, the shadow prime minister, although they don't use that terminology.