Disneyland's version is closing for 10+ months, from January 2008 until November 2008.
The Disneyland version still uses the original flume and boat fleet from the 1964 New York World's Fair, and they are replacing it all because Americans are much fatter today than they were in the 1960's. The boats are too heavy now even with some seats purposely left empty by the CM's, and the heavy boats get stuck inside the ride.
Al Lutz covered this and broke the news on this weighty issue on October 9th on his Miceage website, and now media all over the country is picking up on it and mentioning it too. Even Jay Leno in his Tonight Show monologue. :lol:
The Walt Disney World version of the ride is not affected, and will not be closing.