more than it does in real life, at least for F1 type cars.
Here's a sample video of David Coulthard in a 2002 F1 McLaren, at Spa, running
with a qualifying setup, and a sub 1:45 lap time. Not only does he clip almost
every curb, but he also shoots the bus stop going over both curbs (but staying
within the green pavement). (Since it was rough on the cars, they changed the
bus stop to be a chicane with a short straight). I've have yet to see a sim
where the curbs produce so little effect on a car.
http://www.racesimcentral.net/