GTA IV fix - shut off PSN
It's not the perfect solution, but if you want to stop some the issues plaguing GTA IV, simply sign out of the PlayStation Network before you boot it up.
I can at least somewhat guarantee the success of this method. I was plagued by an endless loading screens upon booting up the game, and I tried everything to remedy the situation - reinstalling the game, deleting the most recent save (out of two), swapping GTA IV discs, playing the game on a separate profile and so on. Nothing worked. Then I signed out of PSN and began the title, and viola, Niko stood amidst the denizens of Liberty City.
As previously mentioned, this may not be a cureall, but it's worth a shot. Unfortunately, even once within the game, you won't be able to access multiplayer (I tried signing in once in GTA IV and the game locked up). Until they release a patch however, this is your best bet to avoid any problems you're having with the game.
These issues have delayed our review of the title, but we'll have one up for you as soon as possible.