Even with the limitations imposed by CSMA/CD things will probably still work if the cable length is too long, it just won't detect collisions correctly, and at a guess a higher level protocol will probably have to request resends because of data corruption. It'll probably work, but the throughput will become pants.
Oh, and well done Maladict(a), people that stupid are the reason that things like my Sagem PVR crashes as soon as you look at it. I wish we had something as powerful as a 100MHz ARM, at the moment most of our code runs on an 8MHz MA31750. Luckily the guy who does are programming for that, will listen to me, and believe me, when I hit him around the head and tell him that it's a really bad idea!