PCWorld obtained an exclusive interview from LastPass CEO that explains what happened and if we should be concerned:
link.
Since they only store salted hashes of your password there is no way an attacker can get to your data using directly what might have been stollen. However, if your password is week (based on dictionary words) the attacker can try to brute-force it.
Their servers didn't experience difficulties because of an attack, but because many people rushed in to change their master password. The best thing to to is change your passwords for important sites. For example go to your banking site an change your password, go to google and change your password, etc. My LastPass plugin works in offline mode at the moment. If you experience difficulties with it, they recommand clearing your cache (Click the LastPass button -> Tools -> Clear Local Cache)