Rockstar has released a patch for the PS3 version of Grand Theft Auto IV
which should help reduce the locking and stuttering issues the game was having. It looks like the culprit was the GameSpy servers as they were getting flooded with requests. Here's the statement from Rockstar
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.