Cosmos-2379, one of the two Russian early-warning satellites that appear to be operational, is drifting off its normal station at 24 degrees West on geosynchronous orbit. The satellite started drifting around August 17 and is moving eastward, which may indicate that it is a controlled transfer to a different station (it hasn't yet reached the closest one at 12E). On the other hand, Cosmos-2379, launched in August 2001, is six years old, which is about the maximum operational life demonstrated by these satellites. So, it is quite possible that Cosmos-2379 completed its mission, leaving only one operational early-warning satellite, Cosmos-2422, launched in July 2006, in orbit.
Russia, meanwhile, is working on a new space-based early-warning system, known as EKS.
UPDATE 09/27/07: Cosmos-2379 seems to have stabilized at the 12E point at about 18-20 September 2007.