Earlier this week many reports came in that both the PS3 and Xbox 360 versions of GTA IV were experiencing freezing problems, with no comment from Take Two or Rockstar at the moment - Sony just recently did.
The problems keep arising for GTA though. In particular, the PlayStation 3 release is being fingered as more likely to have issues with online play, though with the release so fresh out of the door it's hard to pass judgment.
With so many eager people buying the game and plugging it in the instant they get home, it's possible that Sony servers are having trouble coping with the massive number of connections. This could explain why there aren't reports of the 360 version having similar issues, since Microsoft has had a much longer span of time to mature their online service.