It's down for maintenance as they "rebuild" their statistics database. There will be "some minor stats issues" after the downtime but they'll "diminish".
"This is the second phase of the stats database rebuild – this phase is done separately for BFBC2 Xbox 360," . The multiplayer is down right now.
"We are measuring performance both before and after this operation. We expect that there will be some minor stats issues right after the downtime when all the players are getting back online at the same time; this effect will diminish over the following 2 hours."
Here are the times courtesy of EA:
23:00 PM PST Monday – 06:00 AM PST 07:00 AM GMT Tuesday – 14:00 GMT AM 08:00 AM CET Tuesday – 15:00 PM CET
07:00 AM GMT Tuesday – 14:00 GMT AM
08:00 AM CET Tuesday – 15:00 PM CET
DICE's Mikael Kalms hason the forum.