On these servers, having a hacked client is the difference between surviving and being vaporized. If you log into a vanilla Beta 1.7.3 client on a server like "2Beta2Wild" or "AlphaPlace," you will be killed by a fly-hacking, speed-nuking veteran within 60 seconds.
: FastPlace and Nuker (breaks blocks around the player rapidly). Minecraft Beta 1.7.3 Hacked Client