This assumes strong encryption, properly implemented, with no known vulnerabilities (leaving brute force as the only attack option). If they did something stupid, like storing the encryption keys on the same server as the encrypted data, or figuring that XOR would be good enough for encrypting the data, then the encryption is much less meaningful. How much faith one wants to have in Valve's security practices is left as an exercise to each individual.

Here's hoping the encryption can't be broken!

All encryption CAN be broken, it's just a matter of time, usually. In this case, it's just a question of how much you trust Valve with your personal info.

Personally I would be more concerned with using information for social engineering and working to steal accounts that way. This happened recently with some prominent TF2 community members, and I would imagine the information obtained through this hacking incident could certainly aid in future account hijackings.

Additionally, as people already mentioned, it is a bit curious they are even holding on to this information for as long as they have.

I see nothing wrong with posting this here. In fact, I have yet to receive the pop-up notice regarding this I hear others talking about. My friends and I were playing a co-op game earlier today, and only one of us got the message upon closing the game. Had my friend not mentioned it, I certainly wouldn't have known about this otherwise.