Originally Posted by
Si
One thing to bear in mind - I read an article somewhere (and I'm buggered if I can find, it despite lots of searching!) that was highlighting the effect it has on what your car does should the worst happen. Basically, it strengthens a lot of the crumple zones, increasing the forces transmitted to the passenger compartment, and the opinion of the writer was that it shouldn't be done without a cage to protect the passenger 'cell'.
I have no idea how true this is, and if there's any data or empirical or even anecdotal evidence to back it up, but I guess it kind of makes sense and could be worth bearing in mind. It's stopped me doing it to my car TBH.