I wouldnt say game-crippling, but definately dissapointing.  In a big car pileup, there's the chance that if I exit the vehicle that I'm currently in, I'll get stuck in the middle of another car.  It's especially annoying if someone was trying to shoot me, because there wouldnt be anything I could do, they'd shoot through the glass.  Once, I was running from the cops and jumped onto a tanker that had been washed up on the beach.  There was this.... I dunno, some odd structure sticking out towards the top of the boat.  Well I jumped onto it, and immediately got stuck.  The cops ran by, and the game registered that they lost me for a second and then they turned around and started shooting at me.  I couldnt die because I was stuck in that metal object and that's what the bullets kept hitting.  But at the same time, I was stuck, so I had to restart the 360.  Also, I cannot get the aiming or cover system to work in my favor, incredibly annoying.