Hmm. Rockstar released a new Grand Theft Auto IV patch today titled v1.01. Sadly, it doesn't fix those freezing problems but only those multiplayer connectivity issues. Come on Rockstar, I want to actually play it with out worrying it will freeze in the middle of a mission.
[GTA IV gets 1.01 patch, freezing not fixed]
Update: Here is the official release from Rockstar that I just saw in my mailbox. They say it does fix the lock-ups, however.
Rockstar Games has released a GTA IV patch for Playstation 3 today that prevents Gamespy’s servers from being overloaded and therefore reduces the impact on those servers that were causing the game to stutter and lock up. We continue to monitor the performance of the game both on and offline and will provide further updates as necessary. We want to assure everyone that, together with our hardware partners, we continue to strive to give our fans the best possible interactive entertainment experiences possible. This update will ensure that everyone will experience Grand Theft Auto IV the way it was intended. We apologize for the inconvenience this has caused.