I have a Sager NP5793 with 512mb M8800GTX, T9300 and 4GB Ram.
In the lowest widescreen settings (848x480 or something) with everything on low I get between 15 and 30fps.
You can't tell me its the computer, the graphics are worse then GTA3 which runs fine btw.
There's basically no cars and barely anyone on the street because of the low settings so it can't be AI screwing over the CPU surely.
Also with the update I now have no sound effects, only the radio.
Oh, and heres what a real pc game is like,
1920x1200, medium-high settings, antilasing, and still 60fps (admittedly it does drop down to 35 every so often.)