it was supposed to be out already, but they are delaying it to make it "good" to say the least. It's rockstar they barely ever let people down with their games, thats why they are delaying it. they like to put out quality games. and yes it will be tight when it comes out around april.
The demo's they were showing people that were running on 360 with no civilians had framerate issues. It's not so much speculation.. But people say the PS3 is the reason, but framerate was bad on both most likely.
And when I made my previous statement about it being framerates, period.. i didn't mean only framerates.. I'm sure they are having other problems too, with clipping, weird glitches and things like that, which are typical of the open ended games.