Depends, what are you using?
Copper you are limited to 100 meters officially, since its switch to switch you can hit 200 meters. (100bt)
With Gigastack modules I belive the limit is 16 feet, It may even be less as these are diesigned to place the switches directly in the same room. This uses Copper in a firewire style cable.
With Fiber however you can do practicaly unlimited distances, depending on the GBIC. SX, LX, and ZX modules all have different lengths. Anywhere from 500 meters, 2000 meters, or I think 20000 meters.