Hyperbolic
I received both versions this morning (one preorder was half a year ago and I had totally forgotten about it) and while there are differences, it's really minimal. In fact, the time it takes for textures to popin, objects to appear, LODs to change, it's actually variable on both systems. If I left the room and asked somebody else to turn on and play a random version of GTA4 I wouldn't be able to tell which one it was if it weren't for the slightly different color palettes. Some objects appear far in the horizon just fine for the 360 version for example, while the PS3 will struggle itself just to load a fire-hydrant next to you every now and then. It is totally variable and if you really really put an effort into finding the differences, yeah maybe you'll find the PS3 will do a little less struggling every now and then but it is going to require a bit of effort on your part to distinguish the differences.
Port-wise, it is on the same level as Call of Duty 4 and Burnout efforts. Seriously. Because GTA4 is a massive, massive game, and traditional viewpoints are at stake here (such as GTA being a 'PS' game through and through), people will jump onto differences no matter how big or small - and they will stick to them. It's big news when the biggest game of the year hits two major rival consoles in the midst of cheerleaders and fans trying to root for their preferred format of choice. It's a no-brainer to say everyone expected to find differences and shout about them from the rooftops, but GTA4 is by far the biggest example of vastly overstated differences, where one system is the clear superior version and the other one is a bodged job. That's far far far from the actual case here. GTA4 is an excellent textbook case of bloody and decades-long conflict between different platform owners really going the long distance over so little. Even the Halo 3/MGS4 sub-HD resolution controversy nets less attention than this.