Yesterday, I decided to go with MongoHQ for my current project and this morning I saw they got hacked. Irony aside, couple of months back I decided to check AppFog (PaaS) and the next day they were acquired. :)
I believe this is a great time to become a new user of MongoHQ - security has been tightened, experience has been built. The "storm is over" and the chances of a new "storm" in near future (with the measures these guys have taken) have decreased substantially.
I think they reacted pretty impressively, once the breach was detected.
As much as I understood, the biggest flaw in their operations was the fact that many/all internal/support systems were exposed publicly and not within a VPN.
Still, they were around for just about 2 years, which isn't that much time, after all.