It's been offline three times today according to isitdownrightnow.com.

TReano's probably right, it's probably getting DDOS attacked. There's a bitcoin news site that's put a 5 bitcoin bounty out to DOX some DDOS attackers that were threatening its site. The same attackers are probably attacking blockchain.info and a load of other sites unless they pay the attackers off.

http://www.isitdownrightnow.com/blockchain.info.html