As of today, many people have been reporting that they have faced several problems in GTAIV for the PS3 and the 360. For the PS3, the game would freeze during the first opening cutscene of GTAIV. So far this problem occurs mostly for the 20 and 60 gig ps3 users. The 360 on the other hand, would freeze out of no where while you are playing the game. The reason why the 360 and ps3 are freezing is because of the ram. Since Grand theft auto IV is a massive world with no loading points, the ram would be pushed to the limit and cause the cache to overload with information which causes the ps3/360 to freeze. Several people have been reporting that deleting your game save, game data, and cache would fix this problem. Many have done this but they are still facing freezing issues. Rockstar are now aware of these problems and will try to fix it as soon as possible.
P.S. People also reported that their PS3 became bricked after the freezes. Several people received the red ring of doom on their 360 as well.