EDIT: They have a new cert online now. One which hasn't been revoked. The issuer is the same. The new cert was generated two days ago.
EDIT2: Their old cert. The one which was revoked wasn't due to expire for another 323 days. I wonder if this is a precaution in case they actually were hacked and their private ssl key was compromised. Hopefully they'll explain what happened.
EDIT3: Here's a screen grab of the information Certificate Patrol gave me about their old and new certificates side by side: https://grepular.com/lastpass.png
EDIT4: On twitter they are stating: "As a security precaution we acquired a new security certificate, they revoked our old one a bit too soon. Fixed" - https://twitter.com/lastpass
EDIT5: Their latest tweet: "Our new SSL cert is active, this was a planned security upgrade : In the words of the Hitchiker's Guide to the Galaxy, DON'T PANIC."
Checking out their latest blog post from 4 days ago: http://blog.lastpass.com/2011/05/lastpass-security-notificat... it says:
"Multiple security experts and firms were brought in to help us, we've engaged one firm to do a further source code based review."
I'm guessing one or more of these security experts advised that they should get their certificate revoked and replaced purely as a precaution. The new cert has the same expiry date as the old one.