The World Team Championship is kind of like an uber-Olympiad, where the leading teams get to play without having to bother themselves with the riff-raff. Well that was the intention when it was set up, but it has never quite achieved that aim. The 2010 edition is under way in Turkey, although there are already problems with the event.
The teams that qualified to play were the 4 Continental Champions (Asia, Europe, Africa and the Americas) , the top 3 teams from the last Olympiad, the host country, and 2 invited teams. There has been some complaints about the fact that Ukraine was not invited (as it was high finisher at the Olympiad), but I think it is more significant that Armenia, Israel and Greece (who were invited), are all playing, given the historical difficulties between Turkey and each of these countries. Indeed the only country who should have played but didn't show was China, and this snub was apparently political.
While the event may not be as important as originally hoped, it did have one significant effect on the Chess Olympiad. In the 2005 tournament Russia was trailing going into the last round and needed a 3.5-0.5 win over China to take gold. It of course did this, and this result is one of the reasons that FIDE moved from game points to match points for the 2008 Olympiad.
More comprehensive coverage of this event, including the format/composition issues can be found here at Chessvibes.